1658. Dipterous insects, more particularly injurious to animals, are the whole family of breeze or whane flies (Tabanid�), bot and gad-flies (�'strid�), and horse flies (Hippoboscid�). The first of these are excessively troublesome to horses and travellers during summer; the valves of their mouths resemble lancets, which they dart into the flesh and immediately draw blood. The Tabanus bovinus (fig. 291. l) and the H�matopota pluvialis (k) are particularly annoying. Of the bot and gad-flies, there are several species, each appropriated to a particular animal. Thus, the bot-fly (�'strus E'qui Clark, a, b), in its larva state (c), inhabits the anal passage of the horse, and is known among farmers by the name of bots: the chrysalis state is passed in the ground, and the perfect fly (a b) appears in the beginning of August. The gad-fly of the ox (�'strus Bovis, d) appears towards the end of summer; the larv� (e) are called by country people warbels or wornils; they are found beneath the skin on the backs of cattle, and occasion large tumours; the chrysalis (f), like that of the last species, undergoes its change in the ground. Sheep are infested by another gad-fly (�. O'vis, g), the grub of which (h) takes its station in the frontal sinuses, and when full grown it falls through the nostrils; it changes to a chrysalis (i), and in two months becomes a fly (g). The horse flies (Hipp. equina) (fig. 293, l) cause much distress to horses in the vicinity of the New Forest, and handfuls may sometimes be taken off the groins and other parts not well covered with hair. The sheep tick (Melophagus ovinus) belongs to the same family as the last insect, although it is destitute of wings and possesses six legs.
