252 INSECT LIFE xvm 



instantly there. Whichever is at the most favour- 

 able point drops upon the vanishing prey, and the 

 thing is done — the egg is laid. 



There is ample evidence that the Bembex is 

 conscious of danger, and knows how disastrous for 

 the future of her nest is the presence of the hated 

 fly ; her long efforts to throw the parasites off her 

 track, her hesitation and flights, leave not a doubt on 

 the subject. How is it then, I ask myself once 

 more, that the enemy of Diptera should allow herself 

 to be annoyed by another Dipteron — a tiny robber, 

 incapable of the least resistance, which, if she chose, 

 she could destroy instantly ? Why, when once free 

 from the prey which hampers her, does she not 

 pounce on these ill-doers ? What is needed to ex- 

 terminate the evil brood around her burrow ? Merely 

 a battle which would take but a few instants. But 

 the harmony of those laws which govern the preser- 

 vation of species will not have it so, and the Bembex 

 will always allow herself to be harassed without ever 

 learning from the famous " struggle for life " the 

 radical means of extermination. I have seen some 

 which, pressed too closely, let fall their prey and 

 flew off wildly, but without any hostile demonstra- 

 tion, although dropping their game left them full 

 liberty of action. The prey, so ardently desired a 

 moment earlier by the Tachinidae, lay on the ground 

 at the mercy of them all, and not one cared about it. 

 It had no value for the flies, whose larvae need the 

 shelter of a burrow. It was valueless also to the 

 Bembex, who came back, felt it for an instant and 

 left it disdainfully. The little break in her custody 

 of it had rendered her suspicious of it. 



