VI THE YELLOW-WINGED SPHEX 85 



burrow the rubbish heaped at the entrance, com- 

 pletely effacing all outward trace of her work. 

 Three cells are usually found in each burrow, rarely 

 two, and yet more rarely four. As one learns by 

 dissecting the insect, one may estimate the number 

 of eggs laid at about thirty, which would make the 

 number of burrows needed ten. Now these are 

 hardly begun before September, and are finished 

 before the end of the month. Consequently the 

 Sphex cannot devote more than two or three days 

 at most to each burrow and its stores. Evidently the 

 active little creature has not a minute to lose, when 

 in so short a time she has to hollow out the lair, 

 procure a dozen crickets, sometimes brought from a 

 distance through endless difficulties, to store them, 

 and finally to stop up the burrow. Moreover, there 

 are days when wind makes hunting impossible ; 

 rainy days or overcast ones suspending all work. 

 The Sphex cannot give to her building the enduring 

 solidity that Cerceris tuberculata gives to its deep 

 galleries. This species transmit their solid abodes 

 from one generation to another, each year hollowed 

 more deeply, so that I was often bathed in perspira- 

 tion when I tried to reach them, and frequently my 

 efforts and my implements proved useless. The Sphex 

 inherits nothing, and must herself do everything, and 

 that rapidly. Her dwelling is but a tent, hastily erected 

 and moved on the morrow. In compensation the 

 larvae, covered but by a thin layer of sand, know 

 how to supply the shelter which their mother has 

 not given them ; they can clothe themselves with a 

 double and triple waterproof covering, far superior to 

 the thin cocoon of the Cerceris. 



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