88 INSECT LIFE vi 



If they look sharp, they may very well profit by the 

 Sphex's momentary absence from her victim to 

 confide their posterity to it. What yet greater 

 danger menaces the Sphex which renders this pre- 

 liminary descent to the bottom of the burrow such 

 an imperious necessity? 



The one observed fact which can throw any 

 light on the problem is this. Amid a colony of 

 Sphegida; in full activity, whence all other Hymenop- 

 tera are habitually excluded, I one day surprised a 

 sportsman of a different kind, Tachytes nigra, carry- 

 ing one by one, without any haste and with the 

 greatest composure, amid the crowd where he was 

 but an intruder, grains of sand, little bits of dry 

 stalk, and other small materials, to stop up a burrow 

 of the same shape and size as the neighbouring ones 

 of the Sphegidae. This labour was pursued too 

 conscientiously to admit of any doubt as to the 

 presence of the worker's egg in the underground 

 dwelling. A Sphex with anxious movements, 

 apparently the legitimate owner of the burrow, 

 never failed each time that the Tachytes entered 

 the gallery to dart in pursuit, but emerged swiftly, 

 as if frightened, followed by the other, who con- 

 tinued her task unmoved. I visited this burrow, 

 the evident cause of strife between them, and found 

 a cell provisioned with four crickets. Suspicion 

 almost gave place to certainty, for this allowance 

 far exceeded the needs of a Tachytes' larva, which 

 is at least one-half smaller than the Sphex. The 

 calm insect whose care to stop up the burrow 

 at first suggested that it was the owner was really a 

 usurper. How comes it that the Sphex, larger and 



