Her strong, spiny legs, her powerful body filled with strong wing muscles, and her sharp beak, make this robber fly one of the most dreaded enemies of the other winged insects for, like the hawk among the birds, she pounces on them in their flight and tears them to pieces with her beak, sucking the blood from them as she carries them in the air. A single one of these insect hawks, or robber flies, as they are called, has been known to catch and devour as many as eight moths in twenty minutes. These robber flies are fearless creatures, for they attack and kill bumble bees and wasps and even, it is said, that monster demon, the dragon-fly. Tiger beetles, too, are said to fall a prey to this insect hawk. Its other or larval self is also predaceous, boring into beetle larvæ in the ground. [Illustration] A ROBBER FLY (_Dasyllis grossa_, Fab.) When I learned that this powerfully winged, hairy fly tears beetles' wings from off their backs with that wedge-shaped beak of hers, and sucks the blood of bees and wasps, it gave me a different idea of the great fly family, which hitherto I had thought was made up of defenseless creatures like the house fly. Of all the insects we have photographed, few have seemed to be more thoroughly fearless or more ugly than the robber flies. I have never seen one capture and devour a creature larger than itself, but it must be as thrilling an adventure as to see a dragon-fly devour a gnat, or a spider pounce upon the prey entangled in its net. [Illustration] ANOTHER VIEW OF THE ROBBER FLY (_Dasyllis grossa_, Fab.) At first it looked as though this creature had two heads, one at each end of its body, but the great facet eyes, of which only one can be seen in the photograph, make it clear which is the head and which the egg-laying end of this strange, fearless robber of the air. Just why it is called a robber fly when it really doesn't rob at all, but kills, is a mystery to me. [Illustration] ONE OF THE LARGE ROBBER FLIES (_Mallophora sp._) This robber fly is not so quick nor so savage as many of its family. It waits for some slow moving insect to come along then pounces upon it. It probably breeds in decaying wood, although this is not certainly known, and it is very difficult to breed them artificially. To the economic entomologist the ability to breed these monsters in captivity is one of the most important factors in studying out their life histories, as they are called, their various stages, the plants they feed on, their habits of moulting, of breeding and of feeding their young. [Illustration] ONE OF THE WORST OF THE ROBBER FLIES (_Deromyia_) This creature is very savage and pounces upon even large sized insects, paralyzing them instantly by a sting of its poisoned beak. [Illustration] THE CULEX MOSQUITO (_Culex sp._)