Grasshoppers Like Chameleons

There is a jet-black grasshopper that turns sky-blue at sunrise. The curious creature is found on the summit of Mount Kosciusco, highest peak in Australia, where snow lingers into late summer and nights are bitter cold.

The insect is of peculiar interest because of a temperature control mechanism otherwise unknown in nature. Several animals, notably chameleons and some fish, can change color, usually to match their environment. The changes are brought about by certain hormones, released by stimulation of the eyes, which activate different color cells in the skin. But in this grasshopper every one of the outer layer of cells of the body is a color cell. On the surface are granules of black pigment, underneath granules of blue. These change places in response to temperature changes. At approximately 25 degrees C. the blue granules rise to the top, displacing the black. At 15 C. the reverse happens. This displacement can be brought about only by temperature change. Australian entomologists have in vain tried every other sort of stimulus, including illumination with various wave lengths of light.

The phenomenon probably is protective. Seemingly because it is very cold at night on the high mountaintop the black pigment absorbs and retains all the heat available. It is as if the grasshopper carried a woolen blanket. With sunrise an abrupt change takes place; and the days often become intensely hot. If the black coat were retained, the grasshopper would become overheated and probably die. The blue reflects much of the heat.

With the first streaks of sunlight grasshoppers which have slept all night at the foot of grass stalks begin creeping slowly upward. There apparently is no nervous control of the color change. Each color cell seems to act independently. The same reaction takes place in dead grasshoppers when the temperature changes, affecting even fragments of their bodies. It is possible to get a grasshopper half black and half blue by heating one end and cooling the other.