Volume 2 — LETTER XXIII. (continued 2)

Other insects walk, as it were, in the water, moving their legs much in the same way as they would do on the land. Many smaller species of water-beetles, belonging to the genera Hydrophilus, Elophorus, Hydræna, Parnus, Limnius, &c. thus win their way in the waves.—Thus also the water-scorpion (Nepa) pursues its prey; and the little water-mites (Hydrachna) may be seen in every pool thus working their little legs with great rapidity, and moving about in all directions.—Some spiders also will not only traverse the surface of the waters, but, as you have heard with respect to one[581], descend into their bosom. There are other insects moving in this way that are not divers. Of this kind are the aquatic bugs (Gerris lacustris, Hydrometra Stagnorum, Velia Rivulorum, &c. Latr.). The first can walk, run, and even leap, which it does upon its prey, as well as swim upon the surface. The second, remarkable for its extreme slenderness, and for its prominent hemispherical eyes—which, though they are really in the head, appear to be in the middle of the body—rambles about in chase of other insects, in considerable numbers, in most stagnant waters. The Velia is to be met with chiefly in running streams and rivers, coursing very rapidly over their waves[582]. The two last species neither jump nor swim.

I am next to say a few words upon the motions of insects that burrow, either to conceal themselves or their young. Though burrowing is not always a locomotion, I shall consider it under this head, to preserve the unity of the subject. Many enter the earth by means of fore-legs particularly formed for the purpose. The flat dentated anterior shanks, with slender feet, that distinguish the chafers (Petalocera)—most of which in their first states live under ground, and many occasionally in their last—enable them to make their way either into the earth or out of it. Two other genera of beetles (Scarites and Clivina, Latr.)[583] have these shanks palmated, or armed with longer teeth at their extremity, for the same purpose. But the most remarkable burrower amongst perfect insects is that singular animal the mole-cricket (Gryllotalpa vulgaris)[584]. This creature is endowed with wonderful strength, particularly in its thorax and fore legs. The former is a very hard and solid shell or crust, covering like a shield the trunk of the animal; and the latter are remarkably fitted for burrowing, both by their strength and construction. The shanks are very broad, and terminate obliquely in four enormous sharp teeth[585], like so many fingers: the foot consists of three joints—the two first being broad and tooth-shaped, and pointing in an opposite direction to the teeth of the shank; and the last small, and armed at the extremity with two short claws. This foot is placed inside the shank, so as to resemble a thumb and perform the office of one[586]. The direction and motion of these hands, as in moles, is outwards; thus enabling the animal most effectually to remove the earth when it burrows. By the help of these powerful instruments, it is astonishing how instantaneously it buries itself. This creature works under ground like a field-mouse, raising a ridge as it goes; but it does not throw up heaps like its name-sake the mole. They will in this manner undermine whole gardens; and thus in wet and swampy situations, in which they delight, they excavate their curious apartments, before described. The field-cricket (Gryllus campestris) is also a burrower, but by means of different instruments; for with its strong jaws, toothed like the claws of a lobster, but sharper, in heaths and other dry situations it perforates and rounds its curious and regular cells. The house-cricket (G. domesticus), which, on account of the softness of the mortar, delights in new-built houses, with the same organs, to make herself a covered-way from room to room, burrows and mines between the joints of the bricks and stones[587].

But of all the burrowing tribes, none are so numerous as those of the order Hymenoptera. Wherever you see a bare bank, of a sunny exposure, you always find it full of the habitations of insects belonging to it;—and besides this, every rail and old piece of timber is with the same view perforated by them. Bees; wasps; bee-wasps (Bembex); spider-wasps (Pompilus); fly-wasps (Mellinus, Cerceris, Crabro), with many others, excavate subterranean or ligneous habitations for their young. None is more remarkable in this respect than the sand-wasp (Ammophila), or as it might be better named—since it always commits its eggs to caterpillars which it inhumes—the caterpillar-wasp. It digs its burrows, by scratching with its fore legs like a dog or a rabbit, dispersing with its hind ones, which are particularly constructed for that purpose, the sand so collected[588].

Since most of these burrows are designed for the reception of the eggs of the burrowers, I shall next describe to you the manner in which one of the long-legged gnats, or crane-flies (Tipula variegata,)—a proceeding to which I was myself a witness—oviposits. Choosing a south bank bare of grass, she stood with her legs stretched out on each side, and kept turning herself half round backwards and forwards alternately. Thus the ovipositor, which terminates her long cylindrical pointed abdomen, made its way into the hard soil, and deposited her eggs in a secure situation. All, however, were not committed to the same burrow; for she every now and then shifted her station, but not more than an inch from where she bored last. While she was thus engaged, I observed her male companion suspended by one of his legs on a twig, not far from her. The common turf-boring crane-fly (T. oleracea), when engaged in laying eggs, moves over the grass with her body in a vertical position, by the help—her four anterior legs being in the air—of her two posterior ones, and the end of her abdomen, which performs the office of another. Whether in boring, like T. variegata, she turns half round and back, does not appear from Reaumur's account[589].

I now come to motions whose object seems to be sport and amusement rather than locomotion. They may be considered as of three kinds—hovering—gyrations—and dancing.

You have often in the woods and other places seen flies suspended as it were in the air, their wings all the while moving so rapidly as to be almost invisible. This hovering, which seems peculiar to the aphidivorous flies, has been also noticed by De Geer[590]. I have frequently amused myself with watching them; but when I have endeavoured to entrap them with my forceps, they have immediately shifted their quarters, and resumed their amusement elsewhere. The most remarkable insects in this respect are the sphinxes, and from this they doubtless took their name of hawk-moths. When they unfold their long tongue, and wipe its sweets from any nectariferous flower, they always keep upon the wing, suspending themselves over it till they have exhausted them, when they fly away to another. The species called by collectors the humming-bird (Macroglossa Stellatarum), and by some persons mistaken for a real one, is remarkable for this, and the motion of its wings is inconceivably rapid[591].

The gyrations of insects take place either when they are reposing, or when they are flying or swimming.—I was once much diverted by observing the actions of a minute moth upon a leaf on which it was stationed. Making its head the centre of its revolutions, it turned round and round with considerable rapidity, as if it had the vertigo, for some time. I did not, however, succeed in my attempts to take it.—Scaliger noticed a similar motion in the book-crab (Chelifer cancroides)[592].

Reaumur describes in a very interesting and lively way the gyrations of the Ephemeræ before noticed[593], round a lighted flambeau. It is singular, says he, that moths which fly only in the night, and shun the day, should be precisely those that come to seek the light in our apartments. It is still more extraordinary that these Ephemeræ—which appearing after sunset, and dying before sun-rise, are destined never to behold the light of that orb—should have so strong an inclination for any luminous object. To hold a flambeau when they appeared was no very pleasant office; for he who filled it, in a few seconds had his dress covered with the insects, which rushed from all quarters to him. The light of the flambeau exhibited a spectacle which enchanted every one that beheld it. All that were present, even the most ignorant and stupid of his domestics, were never satisfied with looking at it. Never had any armillary sphere so many zones, as there were here circles, which had the light for their centre. There was an infinity of them—crossing each other in all directions, and of every imaginable inclination—all of which were more or less eccentric. Each zone was composed of an unbroken string of Ephemeræ, resembling a piece of silver lace formed into a circle deeply notched, and consisting of equal triangles placed end to end (so that one of the angles of that which followed touched the middle of the base of that which preceded), and moving with astonishing rapidity. The wings of the flies, which was all of them that could then be distinguished, formed this appearance. Each of these creatures, after having described one or two orbits, fell upon the earth or into the water, but not in consequence of being burned[594]. Reaumur was one of the most accurate of observers; and yet I suspect that the appearance he describes was a visual deception, and for the following reason. I was once walking in the day-time with a friend[595], when our attention was caught by myriads of small flies, which were dancing under every tree;—viewed in a certain light they appeared a concatenated series of insects (as Reaumur has here described his Ephemeræ) moving in a spiral direction upwards;—but each series upon close examination, we found was produced by the astonishingly rapid movement of a single fly. Indeed, when we consider the space that a fly will pass through in a second, it is not wonderful that the eye should be unable to trace its gradual progress, or that it should appear present in the whole space at the same instant. The fly we saw was a small male Ichneumon.

Other circular motions of sportive insects take place in the waters. Linné, in his Lapland tour, noticed a black Tipula which ran over the water, and turned round like a whirlwig, or Gyrinus[596]. This last insect I have often mentioned;—it seems the merriest and most agile of all the inhabitants of the waves. Wonderful is the velocity with which they turn round and round, as it were pursuing each other in incessant circles, sometimes moving in oblique, and indeed in every other direction. Now and then they repose on the surface, as if fatigued with their dances, and desirous of enjoying the full effect of the sun-beam: if you approach they are instantaneously in motion again. Attempt to entrap them with your net, and they are under the water and dispersed in a moment. When the danger ceases they reappear, and resume their vagaries. Covered with lucid armour, when the sun shines they look like little dancing masses of silver or brilliant pearls[597].

But the motions of this kind to which I particularly wish to call your attention, are the choral dances of males in the air; for the dancing sex amongst insects is the masculine, the ladies generally keeping themselves quiet at home. These dances occur at all seasons of the year, both in winter and summer, though in the former season they are confined to the hardy Tipulariæ. In the morning before twelve, the Hopliæ, root-beetles before mentioned, have their dances in the air, and the solstitial and common cockchafer appear in the evening—the former generally coming forth at the summer solstice—and fill the air over the trees and hedges with their myriads and their hum. Other dancing insects resemble moving columns—each individual rising and falling in a vertical line a certain space, and which will follow the passing traveller—often intent upon other business, and all unconscious of his aërial companions—for a considerable distance.

Towards sun-set the common Ephemeræ (E. vulgata), distinguished by their spotted wings and three long tails (Caudulæ), commence their dances in the meadows near the rivers. They assemble in troops, consisting sometimes of several hundreds, and keep rising and falling continually, usually over some high tree. They rise beating the air rapidly with their wings, till they have ascended five or six feet above the tree; then they descend to it with their wings extended and motionless, sailing like hawks, and having their three tails elevated, and the lateral ones so separated as to form nearly a right angle with the central one. These tails seem given them to balance their bodies when they descend, which they do in a horizontal position. This motion continues two or three hours without ceasing, and commences in fine clear weather about an hour before sun-set, lasting till the copious falling of the dew compels them to retire to their nocturnal station[598]. Our most common species, which I have usually taken for the E. vulgata, varies from that of De Geer in its proceedings. I found them at the end of May dancing over the meadows, not over the trees, at a much earlier hour—at half-past three—rising in the way just described, about a foot, and then descending, at the distance of about four or five feet from the ground. Another species, common here, rises seven or eight feet. I have also seen Ephemeræ flying over the water in a horizontal direction. The females are sometimes in the air, when the males seize them, and they fly paired. These insects seem to use their fore-legs to break the air; they are applied together before the head, and look like antennæ.—Hilara maura, a little beaked fly, I have observed rushing in infinite numbers like a shower of rain driven by the wind, as before observed[599], over waters, and then returning back.

It is remarkable that the smaller Tipulariæ will fly unwetted in a heavy shower of rain, as I have often observed. How keen must be their sight, and how rapid their motions, to enable them to steer between drops bigger than their own bodies, which, if they fell upon them, must dash them to the ground!

Amidst this infinite variety of motions, for purposes so numerous and diversified, and performed by such a multiplicity of instruments and organs, who does not discern and adore the Great First Mover? From him all proceed, by him all are endowed, in him all move: and it is to accomplish his ends, and to go on his errands, that these little but not insignificant beings are thus gifted; since it is by them that he maintains this terraqueous globe in order and beauty, thus rendering it fit for the residence of his creature man.

I am, &c.