CANNIBAL WASPS 89 



While the cannibal is abroad in search of a victim, this creature, 

 which we will call the checker-fly, 1 because of the peculiar pattern 

 upon her abdomen, takes her life in her hands and slips into the 

 den of the murderer. 



Now to understand this action we must first examine a checker- 

 fly in the laboratory. Dissection brings a wonderful fact to light. 

 In the fly's abdomen we find no eggs, as one might expect, but in their 

 place ten living larvae! The microscope shows them to be whitish 

 maggots clustered together in a ring, and through their transparent 

 bodies one may see the expanding and contracting of embryonic 

 muscles. 



The checker-fly then gives birth to her young alive! But why? 

 She is a lowly rung in the ladder of insect life, while the cannibal, 

 a member of the highest order of insects, is gifted with nothing more 

 unusual than egg laying! 



The explanation is simple. When the checker-fly enters the bur- 

 row, she heads straight for the cell, in order to bear her young upon 

 the meat stored up by the wasp for her own offspring. Thus she 

 saves herself the trouble of providing a home and food for them. 



We must know that the wasp is nearly four times as large as the 

 fly and greatly superior in strength. Now should the fly and the wasp 

 both lay eggs, the ultimate result would be at once apparent. 



The eggs of both insects would hatch about the same time, but 

 the young cannibals would soon grow much larger than the flylets. 

 The strongest individuals survive, and were it not for nature's care 

 in such matters, the young checker-flies would perish. 



What takes place is plain. The parent fly bears her young alive 

 and they start at once feeding and groxving within the cell. In two 

 days the wasp's eggs hatch, but the young checker-flies have now 



1 A species of Tachininae. This sub-family includes some of the most highly 

 beneficial species of flies, such as the Red-tailed Tachina (Winthemia 4-pustulata), 

 a parasite of the Army worm. 



