Soldier Flies

(Family Stratiomyiidae.)

There are certain rather broad, but rather flat-bodied flies of divers structure, but separated from other flies by the characters given in the table, which are not especially remarkable in their appearance except in some aberrant forms, and which are not especially numerous or notable, which are grouped together in this family. Comstock has called them the "soldier flies," on account of bright colored stripes with which some species are marked. They are also dark colored and metallic and are not hairy or bristly. Some of the brightly marked ones look like Syrphus flies and some of them have a superficial resemblance to some of the solitary wasps. The wings are usually clear, but are sometimes smoky or brown. They are found generally in marshy places on flowers and vegetation, and their larvae live in the water, in the earth, in moss, in decaying wood, and in ants' nests, and there are observations on record which seem to show that the larvae of the curious American genus Hermetia may live in bee hives, and in the nests of wild bees. At all events, H. illucens has been seen hovering about bee hives and thrusting its eggs through cracks in the hives. The aquatic species are not confined to fresh water, but at least one is known to inhabit salt water, and one form lives in some of the alkaline lakes of the western states.

Some of the larvae are carnivorous, while others feed upon decaying vegetable matter.

The aquatic forms feed upon very small aquatic organisms. The eggs are laid in overlapping layers upon the under sides of the leaves of aquatic plants, or they are laid upon the surface of the water. The larvae are elongate pointed and flattened. We hardly know enough about the development of any one North American form to draw up a typical life history, but several of the aquatic and subaquatic species have been studied by Hart in his interesting investigations of the entomology of the Illinois River. He finds that Stratiomyia seems to prefer the shore and Odontomyia the water. The larvae are large, opaque, greenish brown or gray, obscurely striped, and when in the water are found upon vegetation near the surface or floating about, and when on shore crawling about over the mud and in the green scum so often found on wet banks. The pupa is formed within the larval skin, but occupies only the head-end, the remainder of the skin being filled with air which causes the pupa to float at the surface of the water. When the fly is ready to emerge the larval skin splits transversally on the fourth segment and the fly emerges while the case is floating on the water or resting on the shore. Hibernating larvae and pupae are found in large numbers on loose drift on the shore, emerging, in Illinois, in early summer. Hart thinks there are two generations annually. He watched the egg-laying of Odontomyia cincta and O. vertebrata. They chose dead branches in the water, reeds and the stems of various plants. The female generally stood with the head downwards, and the long and narrow eggs were placed in an irregular oval mass to the number of several hundred closely laid with their tapering ends inserted between the ends of those next to them.

The larvae and pupae are frequently parasitized by certain Chalcis flies (Smicra rufofemorata and S. microgaster.) Hart made an extremely interesting observation when he found the latter parasite mutilating with its jaws an egg mass of one of these flies. I know of no observation parallel to this. The eggs above referred to were laid June 1st, and hatched in ten days. The stomachs of the larvae were found to contain mud for the most part, with a little vegetable matter, and here and there a diatom.

About one thousand species of Stratiomyiidae have been described, of which about two hundred are found in North America.