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Families Micropezidae, Sepsidae, Psilidae and Diopsidae

The Micropezid flies are slender, dark creatures of a good size, with a few spots on the wings. They are rather awkward in shape, their legs being long, and they are not common. Nothing is known of their metamorphoses, but they are captured upon decaying and foul vegetable and animal matter.

The Sepsidae comprise a series of small, frequently shining black flies, of rather slender form, which breed, as a rule, in decaying vegetable material or in dung. The little shining black species of the genus Piophila, however, breed in cheese, ham fat, and in other fatty or spoiled and decaying animal matter. The little maggot known as the "cheese skipper" is the larva of Piophila casei Linn. This insect frequently does great damage in packing establishments. The eggs are laid in compact clusters of from five to fifteen, or are scattered singly. Each female lays about thirty eggs. The egg is white, slender, slightly curved, one millimeter long, and hatches in thirty-six hours. The larva is cylindrical and tapers toward the anterior end. It completes its growth in from seven to eight days, and if the food supply is sufficient, it does not move much, but when mature it jumps in an extraordinary way, from which it derives its name of cheese skipper. The leap is made by bringing the two ends of the body together, and suddenly releasing them like a spring. In this way they sometimes jump three or four inches. When full grown it moves away to some dry spot, contracts and assumes a yellowish color, the skin hardens, and within the last larval skin the pupa is formed. In ten days the adult fly issues. As a cheese insect in this country this fly does not play as important a part as it does as an enemy to smoked meat. In Europe, it is noted principally as a cheese pest, and it is a matter of common observation that the mother fly seems to prefer the older and richer cheeses in which to deposit her eggs. Her taste is excellent, and, while it is a fair thing to say that skippery cheese is usually the best, it will hardly do to support the conclusion that it is good because it is skippery, although this conclusion is current among a certain class of cheese-eaters. Readers of this will be reminded of the inimitable scene in the Erasmus Inn, described by Charles Reade in "The Cloister and the Hearth."

The flies of the family Psilidae are a little stouter and shorter than the Micropezids, and are sometimes light in color, though generally dark. The metamorphoses of very few of them are known. Some occur in the stems of plants; others are found in the roots of carrots and cabbages, and the flies themselves are seen commonly sitting upon the leaves of bushes and low-growing plants.

The Diopsidae are remarkable from their very curious heads. The head is greatly broadened, with the eyes at the extremities, and the eye-portion is swollen. In some tropical species this feature becomes so exaggerated that the insect looks almost as if it carried bicycle handle bars on its head. They are small black flies, usually stouter than those of the groups which we have just mentioned, and they are found in shady wooded places.