There is a widespread belief that the male always is eaten by the female after mating. Sometimes this happens, but the male never is a willing victim and quite frequently escapes. The eggs are laid in groups of from a dozen to about 400. They are deposited in layers in the midst of a thick frothy liquid which soon hardens and becomes fibrous. For the most part, each species deposits egg masses of a distinctive shape.
On the whole, they probably are beneficial insects because the greater part of their prey consists of species injurious to gardens. The possibility of propagating them for the control of injurious insects, such as Japanese beetles, has been suggested because of their notoriously big appetites. It would, however, be impossible to restrict them to a specific pest. They would continue to eat about every living creature of the right size that came within reach of their claws, including many beneficial species.
Fireflies as Electricians
The flashing of a field of fireflies is an expensive show. For two generations one of the ideals of science has been to produce artificially “cold light”—radiation confined entirely to those wavelengths to which the retina of the human eye is sensitive without any energy being wasted in the form of heat or invisible light. Could the ideal be attained with the same expenditure of fuel and power as is required for light production at present the world’s bills for illumination would be decreased enormously.
Actually the firefly has attained this ideal in one direction. It emits only visible light. From this point of view the firefly or any other sort of luminescent animal is very efficient indeed. A good part of the total radiation from any man-made source of light—or for that matter from the sun—is invisible infrared, observable only as heat. Possibly the firefly produces some heat in its light production but it is too little to be measured. It is safe to say that within a tiny fraction, 100% of the radiation produced is in the visible spectrum—most of it shorter wave lengths than those which produce the sensation of blue light. This is by far the highest efficiency known to science.
Chemists can duplicate the process to a certain extent. Consequently a great deal of research has been devoted to the light-emitting mechanism, physical and chemical, of the insects. Firefly luminescence is due to the oxidation—that is, the burning—of a chemical substance, luciferin. This reaction, in turn, depends upon a catalyst known as luciferase. The same phenomenon can be brought out by appropriate mixtures of luciferin, luciferase, and oxygen in a test-tube at the proper temperature.
All these experiments have shown that, considering the amount of oxygen necessary, it is a very wasteful process. It is far less efficient than most means of producing artificial light known to man—one percent compared with the 4.54 percent of the carbon filament; 17.17 percent of the acetylene flame, or 60 percent of the sodium arc light. To illuminate houses or streets with firefly light would be a very expensive procedure indeed.
Dr. N. D. Maluf of Yale University quotes a calculation that “an area of firefly light six feet in diameter on the ceiling of a room nine feet high would give ample illumination for reading or drawing on a table three feet high.” This would hardly interest an illuminating engineer. The light can, however, be used in an emergency. During the Spanish-American War Major General W. C. Gorgas is reputed to have used the light from a bottle of fireflies to perform an emergency operation. The average householder would rebel at the monthly bills.
The actual light from a single firefly is very minute indeed, averaging little more than 25 thousandths of a candle power. The combined courtship efforts of a whole field full of the insects would hardly light a single room enough for sewing or reading. The insect will sometimes glow steadily with a light as low as two hundred-thousandths of candle power intensity.
Among fireflies, flashing is essentially a courtship phenomenon, yet there is no discernible difference between the quality of the light of male and female insects. What actually happens is that the flash of the female in response to the signal of the male is timed almost exactly at a trifle over two seconds. The male is instinctively aware of this time interval, so that he does not become confused with the signals of other males. In a large group of the insects the flashes of the two sexes tend to become synchronized, producing a field of light.