128 NATURE SKETCHES IN TEMPERATE AMERICA 



nized at once even by the novice, if he will remember that the 

 bumblebee never captures living insects for food. It is only 

 after taking him in hand that his real fly nature becomes 

 evident; for his wings consist of but one pair, instead of two 

 pairs, as in the bees and other Hymenoptera. I found the prey 

 of this robber-fly quite varied in assortment, but it more often 

 consisted of rose-bugs and winged insects. I am informed by 

 C. T. Brues that it also feeds upon bees. 



In the illustration, page 131, I have shown him in mid-air, 

 carrying off a small insect. While I have seen gray-colored 

 species of robber-flies eaten by the phoebe fly-catcher, who 

 decapitates them before feeding them to her young, and have 

 also seen them fall prey to the ant-lions hving in the sand, I 

 have never seen the mimicker of the bumblebee taken as prey 

 by birds or other animals. But Herrick ' records having seen 

 one in the beak of a bluebird, which she fed to her nestlings 

 within a hollow tree. The diet of this bird, however, consists 

 mostly of grasshoppers, katydids, green larvae, and crickets. 



I have shown, in the chapter on the "Quaint Visitors to the 

 Sap Fountains on the Oak," how the flower beetle, Euphoria 

 inda, possibly mimics the bumblebee. The flower beetle, how- 

 ever, enjoys a protective resemblance fo bark and but a 

 partial mimicry to the bee, the latter being more particularly 

 serviceable when on the wing. But in the robber-fly the mim- 

 icry is much more perfected, so that it enjoys all the immunity 

 the bee experiences without possessing a sting. At the same 

 time this mimicry may serve the purpose of facilitating the 

 capture of bees which might fall prey to this insect's rapacious 

 appetite. In the latter case we have what Poulton and others 

 have designated "aggressive mimicry." 



1 "The Home Life of Wild Birds," pp. 73, 74. 



