316 



APPLIED ENTOMOLOGY 



Family Asilidae (The Robber Flies). — These insects as adults prey 

 upon other insects, attacking any species they are able to overcome (Fig. 

 332), but using little discrimination as to the importance to man of their 

 captures. They can hardly be regarded as more than accidentally 

 beneficial to man. Some species (Fig. 333) so closely resemble bumble- 

 bees that a careful examination of the number of wings present is necessary 

 to determine what the insect is. The larvae are found chiefly under bark, 

 in decaying wood or in the ground where decaying vegetable matter occurs, 

 and feed upon insect larvae present in such places. 



Fig. 332. Fig. 333. 



Fig. 332. — Robber Fly {Scleropogon picticornis Loew), about twice natural size. 

 {From U. S. D. A. Bull. 124.) 



Fig. 333. — Bee-like Robber Fly (Dasyllis grossa Fab.), slightly reduced. (Original.) 



This family is one of the largest in the order and its members average 

 large, ranging from a length of about a fifth of an inch to nearly two inches. 



Family Syrphidae (The Syrphus Fhes). — This is one of the largest 

 families of Diptera. The adults range from quite small to rather large 

 insects which visit flowers, feeding on the pollen and nectar, and are most 

 noticeably abundant in bright, sunny weather. They are usually rather 

 brightly colored. 



The larvae of these insects vary greatly in their appearance, live types 

 of them having been recognized. Some are rather flattened, elongate, 

 often green with white spots, and are found with clusters of plant lice on 

 which they feed. Others have nearly cylindrical bodies and bore into 

 the bulbs of various plants. Others live and feed in filth and have short 

 extensible tubes for respiration. Another class which also inhabits filth 

 has extensible respiratory tubes which, when extended to their limit, may 

 be several times the length of the body. Still another group are short, 

 broadly rounded, flattened beneath and high above, somewhat hemispher- 



