FOREST FLY. The British name of a small, widely distributed fly (Hippobosca equina), representing that aberrant division of Diptera styled Eproboscidea (see Fly) and the family Hippoboscidæ. These minute insects are flea-like in appearance and habits, dwelling altogether as parasites among the hairs of animals and feathers of birds, and are sometimes called ‘bird-ticks.’ A common species on large birds in America is Olfersia Americana. Species of another genus, Lipoptera, have wings when young and live upon birds, but after a time they migrate to some mammal, and there, having no further use for their wings, wrench or bite them off. Another genus, Melophagus, includes the wingless sheep-ticks; a whole family, the spider-like bat-ticks (Nycteribiidæ), inhabit the fur of bats alone; and another includes the bee-louse (Braulidæ). All obtain their living by piercing the skin and sucking the blood with an extensile tube thrust out from the mouth. It is in this manner that the forest fly torments horses, especially the short-haired, thin-skinned animals of high breeding. An extraordinary feature in the economy of all these flies is that they do not lay their eggs, but retain them until they hatch into larvæ, and the larvæ are almost ready to pupate; not until then are they extruded by the parent, and only one is produced at a time. Hence the group has been named Pupipara by some systemists.