FIRE-FLIES, any of various forms of noc turnal insects belonging to different orders hav ing the power of voluntary self-luminosity, usually more or less intermittent and exhibited in flashes. After the death of the insects the luminous segments, at least in many forms, can be distinguished by their paler usually yellow color which contrasts with the darker color of the remainder of the insect. The true fire-flies, commonly termed also "lightning bugs,• .are found in the family Lampyrida, and particu larly in the genus Photsnus. Throughout a considerable portion of our country, including the District of Columbia and vicinity, P. pyralis is the most prominent form of fire-fly. Far ther north Pyractomena borealis and related species are the more common fire-flies, while a large species, Photuris pennsylvanica, extends from north to south. One of the most re markable forms of fire-flies is found in the genus Phengodes, in which the females are wingless and larviform; the males are not luminous. The historic and poetic •glow is the wingless female of the European Lampyris noctiluca. In America the glow worms are scarce, and are usually the larva of the genera which have been mentioned, most of which are luminous in both sexes. In other countries various other insects are reported to have the power of luminosity, among which are the lantern-flies of South America (Ful gora lanterneria and candelaria). The lumi nous power of the lantern-fly, however, is doubted. In Central America and the West Indies and in South America the most abun dant fire-flies belong to the genus Pyrophorus, large snapping-beetles (Elaterida), in which the luminous portions of the body are on the sides of the thorax in the form of two large pale eye-like spots. Numerous other forms of insects, including another genus of Elaterida, an Asiatic buprestid beetle, some forms of poduras, the maggots of certain flies, especially of the fungus gnats (Mycetophilidce), are luminous ; but next after the Lampyrider per haps the myriapods are most remarkable for the possession of this power of self-illumina tion. The luminous or photogenic organ is re
garded by Wielowiejsky and also by Emery °as morphologically a specialized portion of the fat body, being a plate consisting of polygonal cells, situated directly under the integument, and supplied with nerves and fine tracheal branches*; while Lang, in writing of the physiology of insect-phosphorescence, briefly states that cells of this luminous organ secrete, under the control of the nervous system, a substance which is burnt during the appearance of the light ; this combustion takes place by means of the oxygen conveyed to the cells of the lumi nous body i by the trachea, which branch pro fusely in it and break up into capillanes? Emery, writing of the luminosity of females of Luciola, states that its use appears to be a means of defense, a warning or danger signal against insectivorous animals, but there is little doubt that it also serves to attract the sexes, especially in the case of the wingless females whose powers of locomotion are so limited, while the males fly freely. Prof. S. P. Langley, secretary of the Smithsonian Institution, has made considerable study of the “cucuj 0' or Pyrophorus, as has also Heinemann, the latter reaching the conclusion that the light depends on a process of oxidation. The cucujos are the most interesting of all the fire-flies, and they are much used by the South and Central Americans in furnishing amusement for the children, while the ladies employ them as ornaments for their evening toilet, fastening great numbers of them to their ball dresses.
The literature of this subject is very exten sive; a list of important articles compiled by A. S. Packard may be found in the of the New York itomological Society (Vol. IV, 1896).