Beetles 



269 



The fireflies are familiar insects which are not flies but beetles, although 

 their soft body and flexible leathery wing-covers are not of the typical 

 coleopterous type. The nocturnal fireflies and their diurnal first cousins, 

 the soldier-beetles, compose a coleopterous family, Lampyridae, of con- 

 siderable size and common distribution over the whole world. The "glow- 

 worm" of England and Europe is the wingless female of a common firefly, 

 and the railway-beetle of Paraguay, a worm-like creature 3 inches long, 

 that emits a strong red light from each end of the body and a green light 

 from points along the sides, is also probably the wingless female of a large 

 firefly species. In this country over 200 species of Lampyridae have been 

 found. Comparatively few of them, however, are luminous. The light- 

 giving organ is usually situated just inside of the ventral wall of the last seg- 

 ments of the abdomen, and consists of a special mass of adipose tissue richly 

 supplied with air-tubes (tracheae) and nerves. From a stimulus conveyed 

 by these special nerves oxygen brought by the network of tracheae is released 

 to unite with some substance of the adipose tissue, a slow combustion thus 

 taking place. To this the light is due, and the relation of the intensity or 

 amount of light to the amount of matter used up to produce it is the most 

 nearly perfect known to physicists. 

 Not only are the adult fireflies 

 luminous, but in some species the 

 pupae and larvae and even the 

 eggs emit light. The combustion 

 in the egg is of course accom- 

 plished wholly without tracheae 

 or controlling nerves. 



The larvae (Fig. 370) of Lam- 

 pyridae mostly burrow under- 



FIG. 370. 



FIG. 371. 



FIG. 372. 



ground, where they feed on soft- FlG - 37 Lara . f fi re%, Photinus modestus. 



' . (Twice natural size.) 



bodied insects, slugs, and Other FIG. 371. Firefly, Photinus scintillans. (Three 

 similar food. The adults, too, times natural size.) 



., ,. , e FIG. 372. Checker-beetle, Trichodes ornatus 



are carnivorous, the diurnal forms, (T $ ce natural size -, 



called soldier-beetles, being com- 

 monly seen on flowers or tree-trunks hunting prey. 



The commoner luminescent fireflies, or "lightning-bugs," belong to the 

 genus Photinus. P. pyralis, the common species from Illinois south, is 

 ^ inch long, blackish, with prothorax with red disk, yellow margin, and black 

 spot in center, and the elytra with narrow yellowish border. Farther north 

 and east the commonest species is P. scintillans (Fig. 371), similar in mark- 

 ing but smaller. P. angulatus, % inch long, is pale, with wide yellow margins 

 on elytra and the margin of the prothorax clouded with black. The com- 

 moner soldier-beetles belong to the genus Chauliognathus, which is char- 



