Flies grasp with their strong legs and claws and then diving their beaks firmly into the bodies of their victims, they suck the blood with great voracity. Next is the life cycle of a fly, the robber fly:
Robber flies belong to one of the largest families of the great order Diptera or two-winged flies. Many of them are of large size, the largest measuring nearly two inches in length.
They are usually hairy, and some of the species are quite robust, resembling the bumblebees in form and color; others are elongate with slender bodies.
The fertilized egg develops within the egg into a young insect, which escapes by bursting the shell or gnawing its way out.
Young insects go through shedding, or ecdysis, several times before they become adults and stop ecdysis permanently.
Most insects shed 4 to 8 times as they grow. The stages between the shedding are defined as instars.
Viewed from the front, the robber’s head is broad, the compound eyes are prominent, and the remainder of the face is hairy and bearded.
The proboscis or beak is stout and strong and is formed for piercing and sucking. Strong in flight, the two wings are long and narrow, while the legs, which are spiny and furnished with stout claws on their toes, are used in grasping their plunder as well as a support for their body when at rest.
These predatory insects rest on the ground, or upon the foliage of plants growing in open sunny spots. Here they lie in wait for their prey, and when a victim in the shape of some other insect appears, they take to the air with a loud, buzzing sound, catching it on the wing.
The unlucky insect, once seized in the powerful grasp of a robber fly, is powerless to escape.
They will attack almost any insect and are even bloodthirsty enough to catch and eat their own kind.
Often they have become a nuisance in making their lair in the vicinity of an apiary, where they kill the honeybees. One of the larger species was observed during the summer capturing a “locust” or cicada.
The robber-fly attacked the cicada on the wing about twenty feet from the ground, and the pair came whirling down. In this case, the booty was too bulky to carry off to some convenient roost, as is generally the case.
Fortunately, robber-flies never attack humans or animals, although if they are carelessly grasped they will sink their lancets into the flesh.
The larvae or “maggots” that hatch from the eggs laid by these flies are also carnivorous. Some of them live in the ground, where they hunt for food among the decaying vegetation; others make their home in rotting logs or beneath loose bark of dying trees, where they hunt and feed upon other soft-bodied insects.
If we follow the fortunes of one of these larvae or “maggots,” we will find that after consuming sufficient food and overwintering, it will go through the usual transformation, emerging finally from the pupal case a perfect robber-fly-and real robber.