Page:Insects - Their Ways and Means of Living.djvu/378

 showing how a primitive ancestral mechanism may be entirely remodeled to serve in a new capacity. If the flies had been specially “created” and not evolved, their structure could have been much more directly fitted to their needs.

It is not only in the matter of wings and the method of flight that the flies show they are highly evolved insects;



they are equally specialized in the structure of their mouth parts and in their manner of feeding. The flies subsist on liquid food. Those species that can satisfy their wants from liquids freely accessible have the mouth parts formed for sucking only. Unfortunately, however, as we all too well know, there are many species that demand, and usu&shy;ally obtain, the fresh blood of mammals, including that of man, and such species have most efficient organs for piercing the skin of their victims.

The most familiar examples of flies that “bite” are the mosquitoes and horseflies. The horseflies (Fig. 169 A), some of which are called also gadflies and deer flies, belong to the family Tabanidae. An examination of the head of