100 BRITISH INSECTS 



serious pests, on account of the annoyance caused to 

 their victims. The males, on the contrary, are rarely 

 seen, and are quite harmless. The great ox gad-fly 1 

 ranks among the largest British Diptera. The larvae 

 of Tabanida are found in water, earth, or decaying 

 wood, where they feed on worms, molluscs, beetle- 

 grubs, etc. 



The alert, hairy robber-flies 2 have been termed the 

 savages of the insect world, since they prey remorse- 

 lessly upon its lesser denizens, and are extremely 

 voracious. A single individual has been observed to 

 kill eight moths in twenty minutes. Indeed, a mem- 

 ber of this family is rarely seen without some other 

 insect in its grasp. Most of our native species are un- 

 attractive ; but A silius wabvoniformis is decidedly hand- 

 some, and has a generalized resemblance to a hornet, 

 Or a large wasp. Like other Asilids, it does not 

 hesitate to attack stinging insects ; but whether its 

 likeness to this class of prey enables it (as has been 

 suggested) to approach its victims without arousing 

 their suspicion, is open to question. Probably the 

 " mimicry " is really protective, serving to exempt the 

 robber itself from the attacks of larger insectivorous 

 creatures. The larvae of robber-flies are found burrow- 

 ing in damp earth. So far as is known, they feed 

 on other insects, especially beetle-grubs. 



The familiar bee-fly 3 is typical of the family Bom- 

 byliidce. Being thick-set and hairy, it might easily be 

 mistaken for a small humble-bee ; but its manner of 

 flight is very characteristic and rapid, and it rests with 

 its wings stretched out on either side. Its mouth- 

 parts, which form a long, stiff proboscis, are of the 

 piercing type, but they are used only for extracting the 



1 Tabanus bovinus. 2 Asilidtz. 3 Bombilius major. 



