XVII HUNTING DIPTERA 235 



while all kept from evaporation in glass tubes, 

 where the air is stagnant, grow mouldy and decay. 

 So they are dead — really dead — when carried to the 

 larva. If some few preserve a little life, a few days, 

 a few hours ends all. Not being clever enough to 

 use its sting, or for some other reason, the assassin 

 kills its victims outright. 



Knowing this complete death of the prey at the 

 moment when it is seized, who would not admire the 

 logic of the Bembecid's manoeuvres ? How method- 

 ical all is, and how one thing brings about another 

 in all which the wary Hymenopteron does ! As the 

 food could not be stored without its decaying at the 

 end of two or three days, it cannot be laid in whole- 

 sale at the beginning of a phase of life destined to 

 last at least a fortnight, and there must be a hunt 

 and distribution of provisions day by day, in pro- 

 portion to the larva's growth. The first ration — that 

 on which the egg is laid — will last longer than the 

 others, and must be small, for the little grub will take 

 several days to eat it, and if too big it would go bad 

 before it was finished. Therefore it will not be a 

 huge gadfly or a corpulent Bombylius, but a small 

 Sphaerophoria, or something of that kind, as a tender 

 meal for a still frail larva. Later, and gradually 

 larger, will come the bigger joints. 



In the mother's absence the burrow must be closed 

 to prevent awkward intrusions, but the entrance must 

 be one opened quickly, without serious difficulty, 

 when the Hymenopteron returns loaded with prey, 

 and laid in wait for by audacious parasites. These 

 conditions would be wanting in a tenacious soil, such 

 as that in which the mining Hymenoptera habitually 



