INSECTS 



Fig. io. A fly whose larvae are parasitic on grass- 

 hoppers, Sarcophaga kellyi. (Much enlarged) 



description of its habits, frequents the fields in Kansas 

 where grasshoppers are abundant. Individuals of this 

 flv, according to Doctor Kelly's account, are often seen 



to dart aftergrass- 

 hoppers on the 

 wing and strike 

 against them. 

 The stricken in- 

 sect at once drops 

 to the ground. 

 Examination re- 

 veals no physical 

 injury to the vic- 

 tim, but on a close 

 inspection there 

 may be found ad- 

 hering to the un- 

 der surface of a 

 wing several tiny, soft, white bodies. Poison pills? 

 Pellets of infection? Nothing so ordinary. The things 

 are alive, they creep along the folds of the wing toward 

 its base — they are, in short, young flies born at the instant 

 the body of the mother fly struck the wing of the grass- 

 hopper. But a young fly would never be recognized as the 

 offspring of its parent; it is a wormlike creature, or maggot, 

 having neither wings nor legs and capable of moving only 

 by extending and contracting its soft, flexible body (Fig. 

 182 D). 



In form, the young Sarcophaga kelhi does not differ par- 

 ticularly from the maggots of other kinds of flies, but the 

 Sarcophaga flies in general differ from most other insects 

 in that their eggs are hatched within the bodies of the 

 females, and these flies, therefore, give birth to young 

 maggots instead of laying eggs. The female of Sarcophaga 

 kellyi, then, when she launches her attack on the flying 

 grasshopper, is munitioned with a load of young maggots 

 ready to be discharged and stuck by the moisture of their 



20 



