Volume 1 — LETTER VI.

INJURIES CAUSED BY INSECTS.

INDIRECT INJURIES CONTINUED.

Having endeavoured to give you some idea of the mode in which insects establish and maintain their empire over man and his train of dependent animals, I shall next call your attention to his living vegetable possessions, whether the produce of the forest, the field, or the garden; whether necessary to him for his support, convenient for his use, or ministering to his comfort, pleasure and delight:—and here you will find these little creatures as busily engaged in the work of mischief as ever, destroying what is necessary, deranging what is convenient, marring what is beautiful, and turning what should give us pleasure into an object of disgust.

Let us begin with the produce of our fields.—Bread is called "the staff of life:" yet should divine Providence in anger be pleased to give the rein to the various insects which, in the different stages of its growth, attack the plant producing it, how quickly would this staff be broken! From the moment that wheat begins to emerge from the soil, to the time when it is carried into the barn, it is exposed to their ravages. One of its earliest assailants in this country is that of which Mr. Walford has given an account in the Linnean Transactions, taking it for the wire-worm; but, as Mr. Marsham observed, not correctly; it being probably the larva of some coleopterous insect, perhaps of one of the numerous tribe of Brachyptera or rove-beetles which are not universally carnivorous. This animal was discovered to infest the wheat in its earliest stage of growth after vegetation had commenced; and there was reason to believe that it began even with the grain itself. It eats into the young plant about an inch below the surface, devouring the central part; and thus, vegetation being stopped, it dies. Out of fifty acres sown with this grain in 1802, ten had been destroyed by the grub in question so early as October[270].—Other predaceous Coleoptera will also attack young corn. This is done by the larva of Zabrus gibbus, particularly with respect to wheat. In the spring of 1813 not less than twelve German hides (Hufen), equal to two hundred and thirty English acres, were destroyed by it in the canton of Seeburg, near Halle in Germany; and Germar (who with other members of the Society of Natural History, at that place, ascertained the fact,) suspects that it was the same insect, described by Cooti, an Italian author, which caused great destruction in Upper Italy in 1776.—Not only is the larva, which probably lives in that state three years, thus injurious; but, what one would not have expected, the perfect beetle itself attacks the grain when in the ear, clambering up the stems at night in vast numbers to get at it.—Along with the larvæ of this insect were found, in the proportion of about one fourth, those of another beetle (Melolontha ruficornis), which seemed to contribute to the mischief[271].

Mr. Markwick has given us the history of a fly that attacks wheat in a later period of its growth, which, if it be not indeed the same, appears to be nearly related to the Musca Pumilionis of Bierkander[272], (Oscinis F.) accused by him of being extremely injurious to rye in the spring. Our insect was discovered on the first sown wheats early in that season, making its lodgement in the very heart of the principal stem just above the root, which stem it invariably destroyed, giving the crop at first a most unpromising appearance, so that there seemed scarcely a hope of any produce. But it proved in this and other instances that year (1791) that the plant, instead of being injured, derived great benefit from this circumstance; for, the main stem perishing, the root (which was not hurt) threw out fresh shoots on every side, so as to yield a more abundant crop than in other fields where the insect had not been busy. These flies therefore seem to belong to our insect benefactors; and I should not have introduced them here, had it not been probable that in some instances later in the spring they may attack the lateral shoots of the wheat, and so be injurious. It is also not unlikely that the new progeny, which is disclosed in May, may oviposit in barley or some other spring corn, which would bring the next generation out in time for the wheat sown in the autumn.—These flies are amongst the last, and, in some seasons, the most numerous, that take shelter in the windows of our apartments when the first frosts indicate the approach of winter, previous to their becoming torpid during that season. When this little animal was first observed in England, it created no small alarm amongst agriculturists lest it should prove to be the Hessian fly, so notorious for its depredations in North America; but Mr. Marsham, by tracing out the species, proved the alarm to be unfounded[273]. That there was sufficient cause for apprehension should it have so turned out, what I have formerly stated concerning the latter insect, and the additional facts which I shall now adduce, will amply show.

The ravages of the animal just alluded to, which was first noticed in 1776, and received its name from an erroneous idea that it was carried by the Hessian troops in their straw from Germany, were at one time so universal as to threaten, where it appeared, the total abolition of the culture of wheat; though, by recent accounts, the injury which it now occasions is much less than at first. It commences its depredations in autumn, as soon as the plant begins to appear above ground, when it devours the leaf and stem with equal voracity until stopped by the frost. When the return of spring brings a milder temperature the fly appears again, and deposits its eggs in the heart of the main stems, which it perforates and so weakens, that when the ear begins to grow heavy, and is about to go into the milky state, they break down and perish. All the crops, as far as it extended its flight, fell before this ravager. It first showed itself in Long Island, from whence it proceeded inland at about the rate of fifteen or twenty miles annually, and by the year 1789 had reached 200 miles from its original station. I must observe, however, that some accounts state its progress at first to have been very slow, at the rate only of seven miles per annum, and the damage inconsiderable; and that the wheat crops were not materially injured by it before the year 1788. Though these insect hordes traverse such a tract of country in the course of the year, their flights are not more than five or six feet at a time. Nothing intercepts them in their destructive career, neither mountains nor the broadest rivers. They were seen to cross the Delaware like a cloud. The numbers of this fly were so great, that in wheat-harvest the houses swarmed with them to the extreme annoyance of the inhabitants. They filled every plate or vessel that was in use; and five hundred were counted in a single glass tumbler exposed to them a few minutes with a little beer in it[274].

America suffers also in its wheat and maize from the attack of an insect of a different order; which, for what reason I know not, is called the chintz-bug-fly. It appears to be apterous, and is said in scent and colour to resemble the bed-bug. They travel in immense columns from field to field, like locusts destroying every thing as they proceed: but their injuries are confined to the states south of the 40th degree of north latitude[275]. From this account the depredator here noticed should belong to the tribe of Geocorisæ, Latr.; but it seems very difficult to conceive how an insect that lives by suction, and has no mandibles, could destroy these plants so totally.

When the wheat blossoms, another marauder, to which Mr. Marsham first called the attention of the public, takes its turn to make an attack upon it, under the form of an orange-coloured gnat, which introducing its long retractile ovipositor into the centre of the corolla, there deposits its eggs. These being hatched, the larvæ, perhaps by eating the pollen, prevent the impregnation of the grain, and so in some seasons destroy the twentieth part of the crop[276].

One would think, when laid up in the barn or in the granary, that wheat would be secure from injury; but even there the weevil (Calandra granaria), in its imago as well as in its larva state, devours it; and sometimes this pest becomes so infinitely numerous, that a sensible man, engaged in the brewing trade, once told me, speaking perhaps rather hyperbolically, that they collected and destroyed them by bushels; and no wonder, for a single pair of these destroyers may produce in one year above 6000 descendants.—There are three other insects that attack the stored wheat, which are more injurious to it than even the weevil. One is a minute species of moth (Tinea granella), happily not much if at all known in this country; of which Leeuwenhoek has given us a full history under the name of the wolf. Another is a species of the same genus, at present not named, which, as we are informed by Du Hamel, at one time committed dreadful ravages in the province of Angoumois in France. The third is Trogosita caraboides, a kind of beetle, the grub of which called Cadelle, Olivier tells us, did more damage to the housed grain in the southern provinces of France than either the weevil or the wolf[277].—Here I may just mention a few other insects which devour grains that are the food of man, concerning which I have collected no other facts. The rice-weevil (Calandra Oryzæ) is very injurious to the useful grain after which it is named, as is likewise another small beetle, Lyctus dentatus, F. (Sylvanus, Latr.): and an Indian grain called in the country Joharré, which appears to be a species of Holcus or Milium, is the appropriate food of another species of Calandra[278], which I found abundant in it.

Rye, in this island, is an article of less importance than wheat; but in some parts of the continent it forms a principal portion of the bread-corn. Providence has also appointed the insect means of causing a scarcity of this species of food. The fly before noticed (Oscinis Pumilionis) introduces its eggs into the heart of the shoots of rye, and occasions so many to perish, that from eight to fourteen are lost in a square of two feet.—A small moth also (Margaritia Secalis) which eats the culm of this plant within the vagina, thus destroys many ears[279]. In common with wheat and barley it also suffers from Leeuwenhoek's wolf and the weevil.

Barley likewise, another of our most valuable grains, has several insect foes. The gelatinous larva of a saw-fly (Tenthredo, L.) preys upon the upper surface of the leaves, and so occasions them to wither. Musca Hordei of Bierkander also assails the plant. A tenth part of the produce of this grain, Linné affirms, is annually destroyed in Sweden by another fly, not yet discovered in Britain, (Oscinis Frit,) which does the mischief by getting into the ear, as does likewise O. lineata, F.—A small species of moth described by Reaumur, though not named by Linné, which may be called Tinea Hordei, (Ypsolophus granellus?) devours the grain when laid up in the granary. This fly deposits several eggs, perhaps twenty or thirty, on a single grain; but as one grain only is to be the portion of one larva, they disperse when hatched, each selecting one for itself, which it enters from without at a place more tender than the rest;—and this single grain furnishes a sufficient supply of food to support the caterpillar till it is ready to assume the pupa. Concealed within this contracted habitation, the little animal does nothing that may betray it to the watchful eye of man, not even ejecting its excrements from its habitation; so that there may be millions within a heap of corn, where you would not suspect there was one[280].

I have not observed that oats suffer from insects, except from the universal subterranean destroyer of the grasses, the wire-worm, of which I shall give you a more full account hereafter; and occasionally from an Aphis. The only important grain that now remains unnoticed is the maize or Indian corn. Besides the chintz-bug-fly, a little beetle[281] (Phaleria cornuta) appears to devour it; and it has probably other unrecorded enemies. The Guinea corn of America (Holcus bicolor), as well as other kinds of grain, is, according to Abbott, often much injured by the larva of a moth (Noctua frugiperda, Smith), which feeds upon the main shoot[282].

Next to grain pulse is useful to us both when cultivated in our gardens and in our fields. Peas and beans, which form so material a part of the produce of the farm, are exposed to the attack of a numerous host of insect depredators; indeed the former, on account of their ravages, is one of the most uncertain of our crops. The animals from which in this country both these plants suffer most are the Aphides, commonly called leaf-lice, but which properly should be denominated plant-lice.—As almost every animal has its peculiar louse, so has almost every plant its peculiar plant-louse; and, next to locusts, these are the greatest enemies of the vegetable world, and like them are sometimes so numerous as to darken the air[283]. The multiplication of these little creatures is infinite and almost incredible. Providence has endued them with privileges promoting fecundity, which no other insects possess: at one time of the year they are viviparous, at another oviparous; and, what is most remarkable and without parallel, the sexual intercourse of one original pair serves for all the generations which proceed from the female for a whole succeeding year. Reaumur has proved that in five generations one Aphis may be the progenitor of 5,904,900,000 descendants; and it is supposed that in one year there may be twenty generations[284]. This astonishing fecundity exceeds that of any known animal; and we cannot wonder that a creature so prolific should be proportionably injurious; some species, however, seem more so than others. Those that attack wheat, oats, and barley, of which there are more kinds than one, seldom multiply so fast as to be very noxious to those plants; while those which attack pulse spread so rapidly, and take such entire possession, that the crop is greatly injured, and sometimes destroyed by them. This was the case with respect to peas in the year 1810, when the produce was not much more than the seed sown; and many farmers turned their swine into their pea-fields, not thinking them worth harvesting. The damage in this instance was caused solely by the Aphis, and was universal throughout the kingdom, so that a sufficient supply for the navy could not be obtained. The earlier peas are sown, the better chance they stand of escaping, at least in part, the effects of this vegetable Phthiriasis.—Beans are also often great sufferers from another species of plant-louse, in some districts from its black colour called the Collier, which begins at the top of the plant, and so keeps multiplying downwards. The best remedy in this case, which also tends to set the beans well, and improves both their quality and quantity, is to top them as soon as the Aphides begin to appear, and carrying away the tops to burn or bury them.—In a late stage of growth great havoc is often made in peas by the grub of a small beetle (Bruchus granarius), which will sometimes lay an egg in every pea of a pod, and thus destroy it.—Something similar I have been told (I suspect it is a short-snouted weevil) occasionally injures beans. In this country, however, the mischief caused by the Bruchus is seldom very serious; but in North America another species (B. Pisi) is most alarmingly destructive, its ravages being at one time so universal as to put an end in some places to the cultivation of that favourite pulse. No wonder then that Kalm should have been thrown into such a trepidation upon discovering some of these pestilent insects just disclosed in a parcel of peas he had brought from that country, lest he should be the instrument of introducing so fatal an evil into his beloved Sweden[285]. In the year 1780 an alarm was spread in some parts of France, that people had been poisoned by eating worm-eaten peas; and they were forbidden by authority to be exposed for sale in the market: but the fears of the public were soon removed by the examination of some scientific men, who found the cause of the injury to be the insect of which I am now speaking[286]. Another species of Bruchus (B. pectinicornis) devours the peas in China and Barbary. A leguminous seed, much used when boiled as food for horses in India, known to Europeans by the name of Gram, but in the Tamul dialect called Koloo, and by the Moors Cooltee, is the appropriate food of a fourth kind of Bruchus, related to the last, but having the antennæ, which in the male are pectinated, much shorter than the body. It is, perhaps, B. scutellaris. A parcel of this seed[287] given me by Captain Green was full of this insect, several grains containing two. Molina, in his History of Chili, tells us of a beetle, which he names Lucanus Pilmus, that infests the beans in that country;—a circumstance quite at variance with the habits of the Lucanidæ, which all prey upon timber. This insect was probably a Phaleria, in which genus the mandibles are protruded from the head like those of Lucanus; and one species, as we have seen above, feeds upon maize.

Great profits are sometimes derived by farmers from their crops of clover-seed: but this does not happen very often; for a small weevil, (Apion flavifemoratum,) which abounds every where at almost all times of the year, feeds upon the seed of the purple clover, and in most seasons does the crop considerable damage; so that a plant of the fairest appearance will, in consequence of the voracity of this little enemy, produce scarcely any thing. Another species (Apion flavipes) infests the Dutch or white clover[288]. The young plants of purple clover, when just sprung, are often, as Mr. Joseph Stickney pointed out to me, much injured by the same little jumping beetles (Haltica) that attack the turnips.

But not only, if let loose to the work of destruction, might insects annihilate our grain and pulse; they would also deprive the earth of that beautiful green carpet which now covers it, and is so agreeable and so refreshing to the sight. When you see a large tract of land lying fallow, as is sometimes the case in open districts, with no intervening patches of verdure, how unpleasant and uncomfortable is it to your eye! What then would be your sensations, were the whole face of the earth bare, and not dressed by Flora? But such a state of things would soon take place, if to punish us, or to teach us thankfulness to the great Arbiter of our fate, the insects that feed upon the grass of our pastures were to become as generally numerous as they are occasionally permitted to do. One of the worst of these ravagers is the grub of the common cock-chafer (Melolontha vulgaris.)[289] This insect, which is found to remain in the larva state four years, sometimes destroys whole acres of grass, as I can aver from my own observation. It undermines the richest meadows, and so loosens the turf that it will roll up as if cut with a turfing-spade. These grubs did so much injury about seventy years ago to a poor farmer near Norwich, that the court of that city, out of compassion, allowed him 25l., and the man and his servant declared that he had gathered eighty bushels of the beetle[290]. In the year 1785 many provinces of France were so ravaged by them, that a premium was offered by the government for the best mode of destroying them. They do not confine themselves to grass, but eat also the roots of corn; and it is to feast upon this grub more particularly that the rooks follow the plough.

The larva also of another species of a cognate genus (Hoplia pulverulenta) is extremely destructive in moist meadows, rooting under the herbage, so that, the soil becoming loose, the grass soon withers and dies. Swine are very fond of these grubs, and will devour vast numbers of them, and the rooks lend their assistance.

Amongst the Lepidoptera, the greatest enemy of our pastures is the Charæas Graminis, which, however, is said not to touch the foxtail grass. In the years 1740, 1741, 1742, 1748, 1749, they multiplied so prodigiously and committed such ravages in many provinces of Sweden, that the meadows became quite white and dry as if a fire had passed over them[291]. This destructive insect, though found in this country, is luckily scarce amongst us; but our northern neighbours appear occasionally to have suffered greatly from it. In 1759, and again in 1802, the high sheep farms in Tweedale were dreadfully infested by a caterpillar, which was probably the larva of this moth; spots of a mile square were totally covered by them, and the grass devoured to the root[292].

Most of the insects I have hitherto mentioned attack our crops partially, confining themselves to one or two kinds only; but there are some species which extend their ravages indifferently to all. Of this description is the Pyralis? frumentalis, which moth, Pallas tells us, is an almost universal pest in the government of Kasan in Russia, often eating the greater part of the spring corn to the root[293]. To this we are fortunately strangers; but another, well known by the name of the wire-worm, causes annually a large diminution of the produce of our fields, destroying indiscriminately wheat, rye, oats, and grass[294]. This insect, which has its name apparently from its slender form, and uncommon hardness and toughness, is the grub of one of the elastic beetles termed by Linné Elater lineatus, but by Bierkander, to whom we are indebted for its history, E. Segetis[295], which name is now generally adopted. The late ingenious Mr. Paul of Starston in Norfolk, (well known as the inventor of a machine[296] to entrap the turnip-beetle, which may be applied by collectors with great advantage to general purposes,) has also succeeded in tracing this insect from the larva to the imago state. His grubs produced Elater obscurus of Mr. Marsham, which however comes so near to E. Segetis that it is doubtful whether it be more than a variety. The other species, however, of the genus have similar grubs, many of which probably contribute to the mischief. When told that it lives in its first (or feeding) state not less than five years, during the greatest part of which time it is supported by devouring the roots of grain, you will not wonder that its ravages should be so extensive, and that whole crops should sometimes be cut off by it. As it abounds chiefly in newly broken-up land, though the roots of the grasses supply it with food, it probably does not do any great injury to our meadows and pastures[297].

Here also may be included the larva of the long-legged gnat (Tipula oleracea), known in many parts by the name of the grub, which is sometimes very prejudicial to the grass in marshy lands, and at others not less so to corn. Reaumur informs us, that in Poitou, in certain years, the grass of whole districts has been so destroyed by it, as not to produce the food necessary for the sustenance of the cattle[298]. In many parts of England, in Holderness particularly, it cuts off a large proportion of the wheat crops, especially if sown upon clover-lays[299]. Reaumur concludes from the observations he made that it lives solely upon earth, and consequently that the injury which it occasions, arises from its loosening the roots of corn and grass by burrowing amongst them: but my friend Mr. Stickney, the intelligent author of a treatise upon this insect, is inclined to think from his experiments that it feeds on the roots themselves. However this may be, the evil produced is evident; and it appears too from the observations of the gentleman last mentioned, that this animal is not killed by lime applied in much larger doses than usual[300].

Our national beverage ale, so valuable and heartening to the lower orders, and so infinitely preferable to ardent spirits and tea, is indebted to another vegetable, the hop, for its agreeable conservative bitter. This plant so precious has numberless enemies in the Lilliputian world to which I am introducing you. Its roots are subject to the attack of the caterpillar of a singular species of moth (Hepiolus Humuli), known to collectors by the name of the ghost, that sometimes does them considerable injury[301].—A small beetle also (Haltica concinna) is particularly destructive to the tender shoots early in the year; and upon the presence or absence of Aphides, known by the name of the fly, as in the case of peas, the crop of every year depends; so that the hop-grower is wholly at the mercy of insects. They are the barometer that indicates the rise and fall of his wealth.

If the beer-drinker be thus interested in the history of these animals, equally so is the drinker of tea. Indeed sugar is an article so universally useful and agreeable, that what concerns the cane that produces it seems to concern every one. This also affords a tempting food to insects. The caterpillar of a white moth, called the borer, for destroying which a reward of fifty guineas is offered by the Society of Arts, is in this respect a great nuisance, as is an unknown species of horned beetle[302]. An ant also (Formica analis) makes a lodgement in the interior of the sugar-cane in Guinea, and destroys it.—But the creature of this class most destructive to the sugar-cane, is one of the latter genus that does not devour it, and is therefore improperly called Formica saccharivora by Linné; but, by making its nest for shelter under the roots, so injures the plants that they become unhealthy and unproductive. These insects about seventy years ago appeared in such infinite hosts in the island of Granada, as to put a stop to the cultivation of this plant; and a reward of 20,000l. was offered to any one who should discover an effectual mode of destroying them. Their numbers were incredible. They descended from the hills like torrents, and the plantations, as well as every path and road for miles, were filled with them. Many domestic quadrupeds perished in consequence of this plague. Rats, mice, and reptiles of every kind became an easy prey to them; and even the birds, which they attacked whenever they alighted on the ground in search of food, were so harassed as to be at length unable to resist them. Streams of water opposed only a temporary obstacle to their progress, the foremost rushing blindly on to certain death, and fresh armies instantly following, till a bank was formed of the carcases of those that were drowned sufficient to dam up the waters, and allow the main body to pass over in safety below. Even the all-devouring element of fire was tried in vain. When lighted to arrest their route, they rushed into the blaze in such myriads of millions as to extinguish it. Those that thus patriotically devoted themselves to certain death for the common good, were but as the pioneers or advanced guard of a countless army, which by their self-sacrifice was enabled to pass unimpeded and unhurt. The intire crops of standing canes were burnt down, and the earth dug up in every part of the plantations. But vain was every attempt of man to effect their destruction, till in 1780 it pleased Providence at length to annihilate them by the torrents of rain which accompanied a hurricane most fatal to the other West India Islands. This dreadful pest was thought to have been imported[303]. Besides these enemies, the sugar-cane has also its Aphis, which sometimes destroys the whole crop[304]; and according to Humboldt and Bonpland the larva of Elater noctilucus feeds in it[305].

Two other vegetable productions of the New World, cotton and tobacco, which are also valuable articles of commerce, receive great injury from the depredations of insects. M'Kinnen, in his Tour through the West Indies, states that in 1788 and 1794 two-thirds of the crop of cotton in Crooked Island, one of the Bahamas, was destroyed by the chenille (probably a lepidopterous larva); and the red bug, an insect equally noxious, stained it so much in some places as to render it of little or no value. Browne relates that in Jamaica a bug destroys whole fields of this plant, and the caterpillar of that beautiful butterfly Helicopis Cupido also feeds upon it[306]. That of a hawk-moth, Sphinx Carolina, is the great pest of Tobacco; and it is attacked likewise by the larva of a moth, Phalæna Rhexiæ, Smith[307], and by other insects of the names and kind of which I am ignorant.

Roots are another important object of agriculture, which, however, as to many of them, they may seem to be defended by the earth that covers them, do not escape the attack of insect enemies.—The carrot, which forms a valuable part of the crop of the sand-land farms in Suffolk, is often very much injured, as is also the parsnip, by a small centipede (Geophilus electricus), and another polypod (Polydesmus complanatus), which eat into various labyrinths the upper part of their roots; and they are both sometimes totally destroyed by the maggot of some dipterous insect, probably one of the Muscidæ. I had an opportunity of noticing this in the month of July, in the year 1812, in the garden of our valued friend the Rev. Revett Sheppard of Offton in Suffolk. The plants appeared many of them in a dying state; and upon drawing them out of the ground to ascertain the cause, these larvæ were found with their head and half of their body immersed in the root in an oblique direction, and in many instances they had eaten off the end of it.

America has made us no present more extensively beneficial, compared with which the mines of Potosi are worthless, than the potato. This invaluable root, which is now so universally cultivated, is often, in this country, considerably injured by the two insects first mentioned as attacking the carrot. The Death's-head-hawk-moth (Acherontia Atropos) in its larva state feeds upon its leaves, though without much injury. In America it is said to suffer much from two beetles (Cantharis cinerea and vittata), of the same genus with the blister-beetle[308]; and in the island of Barbadoes some hemipterous insect, supposed to be a Tettigonia, occasionally attacks them. In 1734 and 1735 vast swarms of them devoured almost every vegetable production of that island, particularly the potato, and thus occasioned such a failure of this excellent esculent, especially in one parish, that a collection was made throughout the island for the relief of the poor, whose principal food it forms.

The chief dependence of our farmers for the sustenance of their cattle in the winter is another most useful root, the turnip. And they have often to lament the distress occasioned by a failure in this crop, of which these minor animals are the cause. On its first coming up, as soon as the cotyledon leaves are unfolded, a whole host of little jumping beetles, composed chiefly of Haltica Nemorum, called by farmers the fly[309] and black jack, attack and devour them; so that on account of their ravages the land is often obliged to be resown, and frequently with no better success. It has been calculated by an eminent agriculturist, that from this cause alone the loss sustained in the turnip crops in Devonshire in 1786 was not less than 100,000l.[310] Almost as much damage is sometimes occasioned by a little weevil (Ceutorhynchus contractus) which in the same manner pierces a hole in the cuticle. When the plant is more advanced, and out of danger from these pygmy foes, the black larva of a saw-fly takes their place, and occasionally does no little mischief, whole districts being sometimes nearly stripped by them; so that in 1783 many thousand acres were on this account ploughed up[311].—The caterpillar of the cabbage-butterfly (Pontia Brassicæ) is also sometimes found upon the turnip in great numbers; and Sir Joseph Banks informs me that forty or fifty of the insects before mentioned[312], called by Mr. Walford the wire-worm, have been discovered in October just below the leaves in a single bulb of this plant.—The small knob or tubercle often observable on these roots is inhabited by a grub, which, from its resemblance to one found in similar knobs on the roots of Sinapis arvensis, from which I have bred Ceutorhynchus contractus (Curculio Marsh) and C. assimilis, small weevils nearly related to each other[313]. This, however, does not seem to affect their growth. Great mischief is occasionally done to the young plants by the wire-worm. I was shown a field last summer in which they had destroyed one-fourth of the crop, and the gentleman who showed them to me calculated that his loss by them would be 100l. One year he sowed a field thrice with turnips, which were twice wholly, and the third time in great part, cut off by this insect.—Whether the disease to which turnips are subject, in some parts of the kingdom, from the form of the excrescences into which the bulb shoots, called fingers and toes, be occasioned by insects, is not certainly known[314].

We have wandered long enough about the fields to observe the progress of insect devastation; let us now return home to visit the domains of Flora and Pomona, that we may see whether their subjects are exposed to equal maltreatment. If we begin with the kitchen-garden, we shall find that its various productions, ministering so materially to our daily comfort and enjoyment, almost all suffer more or less from the attack of the animals we are considering.—Thus, the earliest of our table dainties, radishes, are devoured by the maggot of a fly (Anthomyia Radicum), and our lettuces by the caterpillars of several species of moth; one of which is the beautiful tiger-moth (Euprepia Caja), another the pot-herb-moth (Mamestra oleracea), a third anonymous, described by Reaumur as beginning at the root, eating itself a mansion in the stem, and so destroying the plant before it cabbages[315]. And when they are come to their perfection and appear fit for the table, their beauty and delicacy are often marred by the troublesome earwig, which, insinuating itself into them, defiles them with its excrements.—What more acceptable vegetable in the spring than broccoli? Yet how dreadfully is its foliage often ravaged in the autumn by numerous hordes of the cabbage-butterfly! so that, in an extensive garden, you will sometimes see nothing left of the leaves except the veins and stalks.—What more useful, again, than the cabbage? Besides the same insect, which injures them in a similar way, in some countries they are infested by the caterpillar of a most destructive moth (Mamestra Brassicæ), to which indeed I have before alluded[316]; which, not content with the leaves, penetrates into the very heart of the plant[317].—One of the most delicate and admired of all table vegetables, concerning which gardeners are most apt to pride themselves, and bestow much pains to produce in perfection, I mean the cauliflower, is often attacked by a fly, which ovipositing in that part of the stalk covered by the earth, the maggots when hatched occasion the plant to wither and die, or to produce a worthless head[318]. Even when the head is good and handsome, if not carefully examined previous to being cooked, it is often rendered disgusting by earwigs that have crept into it, or the green caterpillar of Pontia Rapæ.

Our peas, beans, carrots, parsnips, turnips, and potatos are attacked in the garden by the same enemies that injure them in the fields[319]; I shall therefore dismiss them without further notice, and point out those which infest another of our most esteemed kinds of pulse, kidney beans. These are principally Aphides, which in dry seasons are extremely injurious to them. The fluid which they secrete, falling upon the leaves, causes them to turn black as if sprinkled with soot; and the nutriment being subtracted from the pods by their constant suction, they are prevented from coming to their proper size or perfection. The beans also which they contain are sometimes devoured by the caterpillar of a small moth[320].—Onions, which add a relish to the poor man's crusts and cheese, and form so material an ingredient in the most savory dishes of the rich, are also the favourite food of the maggot of a fly, that often does considerable damage to the crop.—From this maggot (for a supply of onions containing which I have to thank my friend Mr. Campbell, surgeon, of Hedon near Hull, where it is very injurious, particularly in light soils,) I have succeeded in breeding the fly, which proves of that tribe of the Linnean genus Musca, now called Scatophaga. Being apparently undescribed, and new to my valued correspondent Count Hoffmansegg to whom I sent it, I call it S. Ceparum[321].—The diuretic asparagus, towards the close of the season, is sometimes rendered unpalatable by the numerous eggs of the asparagus beetle (Lema Asparagi), and its larvæ feed upon the foliage after the heads branch out.—Cucumbers with us enjoy an immunity from insect assailants; but in America they are deprived of this privilege, an unascertained species, called there the cucumber-fly, doing them great injury[322].—And, to name no more, mushrooms, which are frequently cultivated and much in request, often swarm with the maggots of various Diptera and Coleoptera.

The insects just enumerated are partial in their attacks, confining themselves to one or two kinds of our pulse or other vegetables. But there are others that devour more indiscriminately the produce of our gardens; and of these in certain seasons and countries we have no greater and more universal enemy than the caterpillar of a moth called by entomologists Plusia Gamma, from its having a character inscribed in gold on its primary wings, which resembles that Greek letter. This creature affords a pregnant instance of the power of Providence to let loose an animal to the work of destruction and punishment. Though common with us, it is seldom the cause of more than trivial injury; but in the year 1735 it was so incredibly multiplied in France as to infest the whole country. On the great roads, whereever you cast your eyes, you might see vast numbers traversing them in all directions to pass from field to field; but their ravages were particularly felt in the kitchen-gardens, where they devoured every thing, whether pulse or pot-herbs, so that nothing was left besides the stalks and veins of the leaves. The credulous multitude thought they were poisonous, report affirming that in some instances the eating of them had been followed by fatal effects. In consequence of this alarming idea, herbs were banished for several weeks from the soups of Paris. Fortunately these destroyers did not meddle with the corn, or famine would have followed in their train. Reaumur has proved that a single pair of these insects might in one season produce 80,000; so that, were the friendly Ichneumons removed, to which the mercy of Heaven has given it in charge to keep their numbers within due limits, we should no longer enjoy the comfort of vegetables with our animal food, and probably soon become the prey of scorbutic diseases[323].—I must not overlook that singular animal the mole-cricket, (Gryllotalpa vulgaris,) which is a terrible devastator of the produce of the kitchen-garden. It burrows under ground, and devouring the roots of plants thus occasions them to wither, and even gets into hot-beds. It does so much mischief in Germany, that the author of an old book of gardening, after giving a figure of it, exclaims, "Happy are the places where this pest is unknown!"

The flowers and shrubs, that form the ornament of our parterres and pleasure-grounds, seem less exposed to insect depredation than the produce of the kitchen-garden; yet still there are not a few that suffer from it. The foliage of one of our greatest favourites, the rose, often loses all its loveliness and lustre from the excrements of the Aphides that prey upon it. The leaf-cutter bee also (Megachile[324] centuncularis), by cutting pieces out to form for its young its cells of curious construction, disfigures it considerably; and the froth frog-hopper (Cercopis spumaria) aided by the saw-fly of the rose (Hylotoma Rosæ) contributes to check the luxuriance of its growth, and to diminish the splendour of its beauty.—Reaumur has given the history of a fly (Merodon Narcissi) whose larva feeds in safety within the bulbs of the Narcissus, and destroys them; and also of another, though he neglects to describe the species, which tarnishes the gay parterre of the florist, whose delight is to observe the freaks of nature exhibited in the various many-coloured streaks which diversify the blossom of the tulip, by devouring its bulbs[325].—Ray notices another mentioned by Swammerdam, probably Bibio hortulana, which he calls the deadliest enemy of the flowers of the spring. He accuses it of despoiling the gardens and fields of every blossom, and so extinguishing the hope of the year[326]. But you must not take up a prejudice against an innocent creature, even under the warrant of such weighty authority; for the insect which our great naturalist has arraigned as the author of such devastation is scarcely guilty, if it be at all a culprit, in the degree here alleged against it. As it is very numerous early in the year, it may perhaps discolour the vernal blossoms, but its mouth is furnished with no instrument to enable it to devour them.

In our stoves and greenhouses the Aphides often reign triumphant; for, if they be not discovered and destroyed when their numbers are small, their increase becomes so rapid and their attack so indiscriminate, that every plant is covered and contaminated by them, beauty being converted into deformity, and objects before the most attractive now exciting only nausea and disgust. The Coccus (C. Hesperidum) also, which looks like an inanimate scale upon the bark, does considerable injury to the two prime ornaments of our conservatories, the orange and the myrtle; drawing off the sap by its pectoral rostrum, and thus depriving the plant of a portion of its nutriment, at the same time that it causes unpleasant sensations in the beholder from its resemblance to the pustule of some cutaneous disease.

I must next conduct you from the garden into the orchard and fruitery; and here you will find the same enemies still more busy and successful in their attempts to do us hurt.—The strawberry, which is the earliest and at the same time most grateful of our fruits, enjoys also the privilege of being almost exempt from insect injury. A jumping weevil (Orchestes Fragariæ) is said by Fabricius to inhabit this plant; but as the same species is abundant in this country upon the beech, the beauty of which it materially injures by the numberless holes which it pierces in the leaves, and has I believe never been taken upon the strawberry, it seems probable that Smidt's specimens might have fallen upon the latter from that tree[327]. The only insect I have observed feeding upon this fruit is the ant, and the injury that it does is not material.—The raspberry, the fruit of which arrives later at maturity, has more than one species of these animals for its foes. Its foliage sometimes suffers much from the attack of Melolontha horticola[328], a little beetle related to the cockchafer: when in flower the footstalks of the blossom are occasionally eaten through by a more minute animal of the same order, Byturus tomentosus, which I once saw prove fatal to a whole crop; and bees frequently anticipate us, and by sucking the fruit with their proboscis spoil it for the table.—Gooseberries and currants, those agreeable and useful fruits, a common object of cultivation both to poor and rich, have their share of enemies in this class. The all-attacking Aphides do not pass over them, and the former especially are sometimes greatly injured by them; their excrement falling upon the berries renders them clammy and disgusting, and they soon turn quite black from it. In July 1812 I saw a currant-bush miserably ravaged by a species of Coccus, very much resembling the Coccus of the vine. The eggs were of a beautiful pink, and enveloped in a large mass of cotton-like web, which could be drawn out to a considerable length. Sir Joseph Banks lately showed me a branch of the same shrub perforated down to the pith by the caterpillar of Æegeria tipuliformis: the diminished size of the fruit points out, he observes, where this enemy has been at work. In Germany, where perhaps this insect is more numerous, it is said to destroy not seldom the larger bushes of the red currant[329]. The foliage of these fruits often suffers much from the black and white caterpillar of Abraxas grossulariata; (this was the case last spring at Hull;) but their worst and most destructive enemy, particularly of the gooseberry, is that of a small saw-fly. This larva is of a green colour, shagreened as it were with minute black tubercles, which it loses at its last moult. The fly attaches its eggs in rows to the underside of the leaves. When first hatched, the little animals feed in society; but having consumed the leaf on which they were born, they separate from each other, and the work of devastation proceeds with such rapidity, that frequently, where many families are produced on the same bush, nothing of the leaves is left but the veins, and all the fruit for that year is spoiled[330].

Upon the leaves of the cherry, which usually succeeds the gooseberry, in common with those of the pear and several other fruit-trees, the slimy larva of another saw-fly (Tenthredo Cerasi) makes its repast, yet without being the cause of any very material injury. But in North America a second species nearly related to it, known there by the name of the slug-worm, has become prevalent to such a degree as to threaten the destruction not only of the cherry, but also of the pear, quince, and plum. In 1797 they were so numerous that the smaller trees were covered by them; and a breeze of air passing through those on which they abounded became charged with a very disagreeable and sickening odour. Twenty or thirty were to be seen on a single leaf; and many trees, being quite stripped, were obliged to put forth fresh foliage, thus anticipating the supply of the succeeding year and cutting off the prospect of fruit[331].—In some parts of Germany the cherry-tree has an enemy equally injurious. A splendid beetle of the weevil tribe (Rynchites Bacchus) bores with its rostrum through the half-grown fruit into the soft stone, and there deposits an egg. The grub produced from it feeds upon the kernel, and, when about to become a pupa, gnaws its way through the cherry, and sometimes not one in a thousand escapes[332]. This insect is fortunately rare with us, and has usually been found upon the black-thorn. The cherry-fly also (Tephritis Cerasi) provides a habitation for its maggot in the same fruit, which it invariably spoils[333].

The different varieties of the plum are every year more or less injured by Aphides; and a Coccus (C. Persicæ?) sometimes so abounds upon them that every twig is thickly beaded with the red semiglobose bodies of the gravid females, whose progeny in spring exhaust the trees by pumping out the sap.

The blossoms of our pear-trees, as we learn from Mr. Knight, are often rendered abortive by the grub of a brown beetle: and a considerable quantity of its fruit is destroyed by that of a small four-winged fly, which occasions it to drop off prematurely[334]. This would seem to be a saw-fly, and is probably the species which Reaumur saw enter the blossom of a pear before it was quite open, doubtless to deposit its eggs in the embryo fruit. He often found in young pears, on opening them, a larva of this genus[335].—A little moth likewise is mentioned by Mr. Forsyth as very injurious to this tree[336].

But of all our fruits none is so useful and important as the apple, and none suffers more from insects, which according to Mr. Knight[337] are a more frequent cause of the crops failing than frost. The figure-of-eight moth (Episema cæruleocephala), Linné denominates the pest of Pomona and the destroyer of the blossoms of the apple, pear, and cherry.—He also mentions another (Tinea Corticella) as inhabiting apple-bearing trees under the bark.—And Reaumur has given us the history of a species common in this country, and producing the same effect, often to the destruction of the crop, the caterpillar of which feeds in the centre of our apples, thus occasioning them to fall[338]. Even the young grafts, I am informed by an intelligent friend[339], are frequently destroyed, sometimes many hundreds in one night, in the nurseries about London, by Curculio Vastator, Marsh., (Otiorhynchus? picipes) one of the short-snouted weevils; and the foundation of canker in full-grown trees is often laid by the larvæ of Semasia Wœberana[340]. The sap too is often injuriously drawn off by a minute Coccus, of which the female has the exact shape of a muscle-shell (C. arborum linearis, Geoffr.), and which Reaumur has accurately described and figured[341]. This species so abounded in 1816 on an apple-tree in my garden, that the whole bark was covered with it in every part; and I have since been informed by Joshua Haworth, jun. Esq. of Hull, that it equally infests other trees in the neighbourhood. Even the fruit of a golden pippin which he sent me were thickly beset with it.—But the greatest enemy of this tree, and which has been known in this country only since the year 1787, is the apple-aphis, called by some the Coccus, and by others the American blight. This is a minute insect, covered with a long cotton-like wool transpiring from the pores of its body, which takes its station in the chinks and rugosities of the bark, where it increases abundantly, and by constantly drawing off the sap causes ultimately the destruction of the tree. Whence this pest was first introduced is not certainly known. Sir Joseph Banks traced its origin to a nursery in Sloane Street; and at first he was led to conclude that it had been imported with some apple-trees from France. On writing, however, to gardeners in that country, he found it to be wholly unknown there. It was therefore, if not a native insect, most probably derived from North America, from whence apple-trees had also been imported by the proprietor of that nursery. Whatever its origin, it spread rapidly. At first it was confined to the vicinity of the metropolis, where it destroyed thousands of trees. But it has now found its way into other parts of the kingdom, particularly into the cyder counties; and in 1810 so many perished from it in Gloucestershire, that, if some mode of destroying it were not discovered, it was feared the making of cyder must be abandoned. This valuable discovery, it is said, has since been made; the application of the spirit of tar to the bark being recommended as effectual[342]. Sir Joseph Banks long ago extirpated it from his own apple-trees, by the simple method of taking off all the rugged and dead old bark, and then scrubbing the trunk and branches with a hard brush[343].

Our more dainty and delicate fruits, at least such as are usually so accounted, the apricot, the peach, and the nectarine, originally of Asiatic origin, are not less subject to the empire of insects than the homelier natives of Europe. Certain Aphides form a convenient and sheltered habitation for themselves, by causing portions of the leaves to rise into hollow red convexities; in these they reside, and, with their rostrum pumping out the sap, in time occasion them to curl up, and thus deform the tree and injure the produce. The fruit is attacked by various other enemies of this class, against which we find it not easy to secure it: wasps, earwigs, flies, wood-lice, and ants, which last communicate to it a disagreeable flavour, all share with us these ambrosial treasures; the first of them as it were opening the door, by making an incision in the rind, and letting in all the rest.—The nucleus of the apricot is also sometimes inhabited by the caterpillar of a moth, which devouring the kernel causes the fruit to fall prematurely[344].—In this country, however, these fruits may be regarded as mere luxuries, and therefore are of less consequence; but in North America they constitute an important part of the general produce, at least the peach, serving both as food for swine, and furnishing by distillation a useful spirit. The ravages committed upon them there by insects are so serious, that premiums have been offered for extirpating them. A species of weevil, perhaps a Rynchites, enters the fruit when unripe, probably laying its eggs within the stone, and so destroys them. And two kinds of Zygæna, by attacking the roots do a still greater injury to the trees[345].—A Coccus, as it should seem from the description, imported about thirty years ago from the Mauritius, or else with the Constantia vine from the Cape of Good Hope, has destroyed nearly nine-tenths of the peach-trees in the Island of St. Helena, where formerly they were so abundant, that, as in North America, the swine were fed with them. Various means have been employed to destroy this plague, but hitherto without success[346].—The imperial pine-apple, the glory of our stoves, and the most esteemed of the gifts of Pomona, cannot, however precious, be defended from the injuries of a singular species of mite, the red Spider[347] of gardeners, (Erythræus telarius) which covers them, and other stove plants, with a most delicate but at the same time very pernicious web.—The olive-tree, so valuable to the inhabitants of the warmer regions of Europe, often nourishes in its berries the destructive maggot of a fly (Oscinis Oleæ); and the caterpillar of a little moth (Tinea Oleella), which preys upon the kernel of the nucleus, occasions them to fall before they are ripe.—Every one who eats nuts knows that they are very often inhabited by a small white grub; this is the offspring of a weevil (Balaninus Nucum) remarkable for its long and slender rostrum, with which it perforates the shell when young and soft, and deposits an egg in the orifice.—In France it sometimes happens, when the chestnuts promise an abundant crop, that the fruit falls before it comes to maturity, scarcely any remaining upon the trees. The caterpillar of a moth which eats into its interior is the cause of this disappointment[348].—Of fruits the date has the hardest nucleus; yet an insect of the same tribe with the above, that feeds upon its kernel, is armed with jaws sufficiently strong to perforate it, that it may make its escape when the time of its change is arrived, and assume the pupa between the stone and the flesh. The date is eaten also by a beetle which Hasselquist calls a Dermestes[349].

One of the most delicious, and at the same time most useful, of all our fruits is the grape: to this, as you know, we are indebted for our raisins, for our currants, for our wine, and for our brandy; you cannot therefore but feel interested in its history, and desire to be informed, whether, like those before enumerated, this choice gift of Heaven, whose produce "cheereth God and man[350]," must also be the prey of insects. There is a singular beetle, common in Hungary, (Lethrus cephalotes) which gnaws off the young shoots of the vine, and drags them backward into its burrow, where it feeds upon them: on this account the country people wage continual war with it, destroying vast numbers[351].—Three other beetles also attack this noble plant: two of them, mentioned by French authors, (Rynchites Bacchus and Eumolpus Vitis,) devour the young shoots, the foliage and the footstalks of the fruit, so that the latter is prevented from coming to maturity[352]; and a third (C. Corruptor, Host,) by a German, which seems closely allied to Otiorhynchus? picipes before mentioned, if it be not the same insect. This destroys the young vines, often killing them the first year; and is accounted so terrible an enemy to them, that not only the animals but even their eggs are searched for and destroyed, and to forward this work people often call in the assistance of their neighbours[353].—In the Crimea the small caterpillar of a Procris or Ino (lepidopterous genera separated from Sphinx, L.) related to I. Statices, is a still more destructive enemy. As soon as the buds open in the spring, it eats its way into them, especially the fruit buds, and devours the germ of the grape. Two or three of these caterpillars will so injure a vine, by creeping from one germ to another, that it will bear no fruit nor produce a single regular shoot the succeeding year[354].—Vine leaves in France are also frequently destroyed by the larva of a moth (Tortrix vitana); in Germany another species does great injury to the young bunches, preventing their expansion by the webs in which it involves them[355]; and a third (Tortrix fasciana) makes the grapes themselves its food: a similar insect is alluded to in the threat contained in Deuteronomy[356].—The worst pest of the vine in this country is its Coccus (C. Vitis). This animal, which fortunately is not sufficiently hardy to endure the common temperature of our atmosphere, sometimes so abounds upon those that are cultivated in stoves and greenhouses, that their stems seem quite covered with little locks of white cotton; which appearance is caused by a filamentous secretion transpiring through the skin of the animal, in which they envelop their eggs. Where they prevail they do great injury to the plant by subtracting the sap from its foliage and fruit, and causing it to bleed.—And to close the list, you are perfectly aware of the eagerness with which wasps, flies, and other insects, attack the grapes when ripe, often leaving nothing but the mere skin for their lordly proprietor.

There are some of these creatures that attack indiscriminately all fruit-trees. One of these is the Cicada septendecim, (so called because, according to Kalm, it appears only once in seventeen years[357].) The female oviposits in the pith of the twigs of trees, where the grubs are hatched, and do infinite damage both to fruit- and forest-trees[358].—Another, the caterpillar of the butterfly of the hawthorn, (Pieris Cratægi) which in 1791, in some parts of Germany, stripped the fruit-trees in general of their foliage[359].—In France also in 1731 and 1732 that of a moth which seems related to the brown-tail moth (Arctia phæorhœa), whose history has been given by the late Mr. Curtis, was so numerous as to occasion a general alarm. The oaks, elms, and white-thorn hedges looked as if some burning wind had passed over them and dried up their leaves; for, the insect devouring only one surface of them, that which is left becomes brown and dry. They also laid waste the fruit-trees, and even devoured the fruit; so that the parliament published an edict to compel people to collect and destroy them; but this would in a great measure have been ineffectual, had not some cold rains fallen, which so completely annihilated them, that it was difficult to meet with a single individual[360].

If we quit the orchard and fruit-garden for a walk in our plantations and groves, we shall still be forced to witness the sad effects of insect devastation; and when we see, as sometimes happens, the hedges and trees entirely deprived of their foliage, and ourselves of the shade we love from the fervid beam of the noon-day sun; when the singing birds have deserted them; and all their music, which has so often enchanted us by its melody, variety, and sweetness, has ceased—we shall be tempted in our hearts to wish the whole insect race was blotted from the page of creation. Numerous are the agents employed in this work of destruction. Amongst the beetles, various cockchafers (Melolontha vulgaris, Amphimalla solstitialis, and Phyllopertha horticola) in their perfect state act as conspicuous a part in injuring the trees, as their grubs do in destroying the herbage. Besides the leaves of fruit-trees, they devour those of the sycamore, the lime, the beech, the willow, and the elm. They are sometimes, especially the common one, astonishingly numerous. Mouffet relates (but one would think that there must be some mistake in the date, since they are never so early in their appearance,) that on the 24th of February 1574 such a number of them fell into the river Severn as to stop the wheels of the water-mills[361]. It is also recorded in the Philosophical Transactions, that in 1688 they filled the hedges and trees of part of the county of Galway in such infinite numbers, as to cling to each other in clusters like bees when they swarm; on the wing they darkened the air, and produced a sound like that of distant drums. When they were feeding, the noise of their jaws might be mistaken for the sawing of timber. Travellers and people abroad were very much annoyed by their continual flying in their faces; and in a short time the leaves of all the trees for some miles round were so totally consumed by them, that at Midsummer the country wore the aspect of the depth of winter[362].

But the criminals to whom it is principally owing that our groves are sometimes stripped of the green robe of summer, are the various tribes of Lepidoptera, especially the night-fliers or moths, myriads of whose caterpillars, in certain seasons, despoil whole districts of their beauty, and our walks of all their pleasure. In 1731 the oaks in France were terribly devastated by the larva of Hypogymna dispar[363], and in 1797 many of the pine forests about Bayreuth suffered a similar injury from that of H. Monacha[364]. Those of Germany are also sometimes laid waste by the caterpillar of a beautiful moth belonging to the Noctuidæ (Achatea spreta[365]), which has been taken in England. Cheimatobia brumata is likewise a fearful enemy to the foliage of almost every kind of tree[366]. The woods in certain provinces of North America are in some years entirely stripped by that of another moth, which eats all kinds of leaves. This happening at a time of the year when the heat is most excessive is attended by fatal consequences. For, being deprived of the shelter of their foliage, whole forests are sometimes entirely dried up and ruined[367].—The brown-tail moth, before alluded to, which occasionally bares our hawthorn hedges, has been rendered famous by the alarm it caused to the inhabitants of the vicinity of the metropolis in 1782, when rewards were offered for collecting the caterpillars, and the churchwardens and overseers of the parishes attended to see them burnt by bushels.—You may have observed perhaps in some cabinets of foreign insects an ant, the head of which is very large in proportion to the size of its body, with a piece of leaf in its mouth many times bigger than itself. These ants, called in Tobago parasol ants (Œcodoma cephalotes), cut circular pieces out of the leaves of various trees and plants, which they carry in their jaws to their nests, and they will strip a tree of its leaves in a night, a circumstance which has been confirmed to me by Captain Hancock[368]. Stedman mentions another very large ant, being at least an inch in length, which has the same instinct. It was a pleasant spectacle, he observes, to behold this army of ants marching constantly in the same direction, and each individual with its bit of green leaf in its mouth[369]. The injury thus caused to trees by insects is not confined to the mere loss of their leaves for one season; for it occasions them to draw upon the funds of another, by sending forth premature shoots and making gems unfold, that, in the ordinary course, would not have put forth their foliage till the following year.

Other insects, though they do not entirely devour the leaves of trees and plants, yet considerably diminish their beauty. Thus, for instance, sometimes the subcutaneous larvæ undermine them, when the leaf exhibits the whole course of their labyrinth in a pallid, tortuous, gradually dilating line—at others the Tortrices disfigure them by rolling them up, or the leaf-cutter bees by taking a piece out of them, or certain Tineæ again by eating their under surface, and so causing them to wither either partially or totally. You have doubtless observed what is called the honey-dew upon the maple and other trees, concerning which the learned Roman naturalist Pliny gravely hesitates whether he shall call it the sweat of the heavens, the saliva of the stars, or a liquid produced by the purgation of the air[370]!! Perhaps you may not be aware that it is a secretion of Aphides, whose excrement has the privilege of emulating sugar and honey in sweetness and purity. It however often tarnishes the lustre of those trees in which these insects are numerous, and is the lure that attracts the swarms of ants which you may often see travelling up and down the trunk of the oak and other trees. The larch in particular is inhabited by an Aphis transpiring a waxy substance like filaments of cotton: this is sometimes so infinitely multiplied upon it as to whiten the whole tree, which often perishes in consequence of its attack. The beech is infested by a similar one. Some animals also of this genus inhabiting the poplar, elm, lime, and willow, reside in galls they have produced, that disfigure the leaves or their footstalks. Perhaps those resembling fruit, or flowers, or moss, produced by the Aphis of the fir (Aphis Abietis), the different species of gall-gnats (Cecidomyia), or occasioned by the puncture and oviposition of the various kinds of gall-flies (Cynips), may be regarded rather as an ornament than as an injury to a tree or shrub; yet when too numerous they must deprive it of its proper nutriment, and so occasion some defect. And probably the enormous wens, and other monstrosities and deformities observable in trees, may have been originally produced by the bite or incision of insects.

Besides exterior insect enemies, living trees are liable to the ravages of many that are interior. The caterpillar of the great goat-moth (Cossus ligniperda[371]), of the hornet hawk-moth (Sesia crabroniformis, F.), and of two beetles (Nitidula grisea, and Cryptorhynchus Lapathi), devour the wood of the willow and sallow, which thus in time often become so hollow as to be easily blown down. The bee hawk-moth (Sesia apiformis[372]), and probably Rynchites Populi, a brilliant green weevil, feeds upon the poplar—Prionus coriarius is sometimes found in the oak and sometimes in the elm, and Hylurgus piniperda[373], in the Scotch fir. Mr. Stephens informs me that the fir-trees in a plantation of Mr. Foljambe's in Yorkshire were destroyed by a hymenopterous insect (Sirex Gigas), while those of another belonging to the same gentleman in Wiltshire met with a similar fate from the attack of Sirex Juvencus. The elm also suffers dreadfully from the attack of another minute beetle (Scolytus destructor), related to the last[374].—When the sap flows from wounds in a tree it is attended by various other beetles, (I have observed Cetonia aurata, and several Nitidulæ and Brachyptera busy in this way,) which prevent it from healing so soon as it would otherwise do; and if the bark be any where separated from the wood, a numerous army of wood-lice, earwigs, spiders, field-bugs, and similar subcortical insects take their station there and prevent a re-union.

The mischief however produced by any or all of these, is not to be compared with that sometimes sustained in Germany from the attacks of a small beetle, (Bostrichus Typographus) so called on account of a fancied resemblance between the paths it erodes and letters, which bores into the fir. This insect, in its preparatory state, feeds upon the soft inner bark only: but it attacks this important part in such vast numbers, 80,000 being sometimes found in a single tree, that it is infinitely more noxious than any of those that bore into the wood: and such is its vitality, that though the bark be battered and the tree plunged into water, or laid upon the ice or snow, it remains alive and unhurt. The leaves of the trees infested by these insects first become yellow, the trees themselves then die at the top, and soon entirely perish. Their ravages have long been known in Germany under the name of Wurm trökniss (decay caused by worms); and in the old liturgies of that country the animal itself is formally mentioned under its vulgar appellation, "The Turk." This pest was particularly prevalent and caused incalculable mischief about the year 1665. In the beginning of the last century it again showed itself in the Hartz forests—it reappeared in 1757, redoubled its injuries in 1769, and arrived at its height in 1783, when the number of trees destroyed by it in the above forests alone, was calculated at a million and a half, and the inhabitants were threatened with a total suspension of the working of their mines, and consequent ruin. At this period these Bostrichi, when arrived at their perfect state, migrated in swarms like bees into Suabia and Franconia. At length, between the years 1784 and 1789, in consequence of a succession of cold and moist seasons, the numbers of this scourge were sensibly diminished. It appeared again however in 1790, and so late as 1796 there was great reason to fear for the few fir-trees that were left[375].

The seeds of forest- as well as of fruit-trees are doubtless subject to injuries from the same quarter, but these being more out of the reach of observation, have not been much noticed. Acorns, however, a considerable article with nurserymen, are said to have both a moth and a beetle that prey upon them; and what is remarkable, though sometimes one larva of each is found in the same acorn, yet two of either kind are never to be met with together[376]. The beetle is probably the Curculio Glandium (Balaninus) of Mr. Marsham, and is nearly related to the species whose grub inhabits the nut.

Having now conducted you round and exhibited to you the melancholy proofs of the universal dominion of insects over our vegetable treasures, while growing or endued with the principle of vitality, in their separate departments,—I must next introduce you to a pest worse than all put together, which indiscriminately attacks and destroys every vegetable substance that the earth produces, and which, wherever it prevails, carries famine, pestilence and death in its train. Happily for this country—and we cannot be too thankful for the privilege, we know this scourge of nations only by report. The name of Locust, which has been such a sound of horror in other countries, here only suggests an object of interesting inquiry. But the ravages of locusts are so copious a theme that they merit to be considered in a separate letter.

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