THE ROBBER-FLIES 



(Family Asilidce.) 



The strong, hairy, active, predatory flies, known as robber- 

 flies, form this group. They are very numerous and are always 

 conspicuous, flying with a darting motion and preying upon 

 many different kinds of insects. They are, as a rule, rather 

 slender, but extremely strong, and are furnished with a large, 

 tapering, hard beak, enclosing a sharp lancet which is thrust out 

 and cuts a severe wound in the body of 

 the insect captured. The tip of the beak 

 is bearded with stiff bristles which hold 

 it securely in the wound into which it is 

 crowded. Fitch says, "These fiies are 

 inhuman murderers. They are savages 

 of the insect world, putting their captives 

 to death with merciless cruelty. Their 

 large eyes, divided into such a multitude 

 of facets, probably give them the most 

 acute and accurate vision for espying and 

 seizing their prey; and their long, stout 

 legs, their bearded and bristly head, their whole aspect indicates 

 them to be of a predatory and ferocious character. Like the 

 hawk, they swoop upon their prey, and grasping it securely be- 

 tween their forefeet they violently bear it away." Nearly all of 

 their victims are captured on the wing, and any flying insect is 

 liable to be caught by them — other flies, bees, beetles, moths, 

 butterflies, grasshoppers, and even members of their own spe- 

 cies, so that they are true cannibals, just as with the praying 

 Mantis, or rearhorse, the female frequently resents the caresses of 

 the male, and grasps him and eats him. They will also feed 

 upon caterpillars, but rarely. Persons engaged in bee culture 

 especially fear these robber-flies, which are known rather gener- 

 ally in this country as bee-killers. One of Dr. Fitch's corre- 



141 



Fig. 80. — Erax bastardi. 

 (After Riley.) 



