The fly lays its eggs in freshly dropped cow manure. They hatch in about 24 hours, and the larvæ or maggots in four or five days develop to the pupal stage, which lasts a week or 10 days. From the pupal stage the mature fly emerges. The entire process of development from the deposition of the egg to the appearance of the mature fly therefore may be completed in two weeks, or even in a shorter time. To protect cattle from attacks of the hornfly they may be treated with one of the remedies mentioned above ([p. 502]). Dipping cattle in a vat provided with splashboards set at the proper angle destroys most of the hornflies present on the animals. Unless the splashboards are used all but a few of the flies succeed in escaping as the cattle plunge into the bath and later return to them. Scattering the droppings of cattle with a shovel, or with brush dragged over pastures, in order to insure the rapid drying of the manure and consequent destruction of the larvæ, is, when practicable, an efficient means of reducing the number of these flies.
Fig. 2.—Hornflies (Lyperosia irritans) on cow horn. (From Bureau of Entomology.)