XVIII A PARASITE— THE COCOON 253 



Let us end this chapter by the history of the 

 larva. Its monotonous life offers nothing remarkable 

 during the two weeks while it eats and grows. 

 Then comes making a cocoon. The slight develop- 

 ment of silk-producing organs does not allow of a 

 dwelling of pure silk, like those of the Ammophila 

 and Sphegidae — made of several wrappers which 

 protect the larva, and later the nymph, from damp in 

 the ill-protected, shallow burrow during autumn rains 

 and winter snows. Yet this Bembex burrow is in 

 worse conditions than those of the Sphex, being 

 made at a depth of only a few inches in very per- 

 meable soil. To fashion a sufficient shelter the 

 larva supplements by its industry the small amount 

 of silk at its disposal. With grains of sand artistic- 

 ally put together and connected by silky matter, it 

 constructs a most solid cocoon — impenetrable to 

 damp. 



Three general methods are employed by fossorial 

 Hymenoptera to construct the dwelling in which 

 metamorphosis is to take place. Some hollow 

 burrows at a great depth under a shelter, and then 

 the cocoon consists of a single wrapper, so thin as to 

 be transparent. Such is the case with Philan- 

 thidae and Cerceris. Others are content with a 

 shallow burrow in open ground ; but in that case 

 they have silk enough for manifold wrappings of the 

 cocoon, as with Sphegidae, Ammophila, and Scolia ; 

 or if the quantity be insufficient, they use agglutin- 

 ated sand — as, for instance, the Bembex and Palarus. 

 One might take a Bembex cocoon for a solid 

 kernel, so compact and resistent is it. The form is 

 cylindrical — one end rounded, the other pointed. 



