BEHAVIOUR 109 



the perfect insect has ultimately to make its way ; in such 

 cases the larva before pupation has the habit of coming 

 close to the surface. The large caterpillar of the Goat Moth 

 (Cossus), for example, feeds for more than a year on wood 

 as it tunnels through the timber of some tree. When fully 

 grown it usually comes to the bark before it makes its cocoon 

 of chips of wood fastened together by its silky secretion. 

 This is an insect whose pupa works its way partly out of 

 the cocoon before undergoing the final moult which releases 

 the moth, and as the cocoon has been formed close to the 

 surface of the tree trunk or branch, the greater part of the 

 pupa's body projects into the air, so that there is, after that 

 moult, no obstacle to the free emergence of the moth. The 

 small larva of a seed-beetle (Bruchus), when hatched from 

 the egg laid on a leguminous blossom, bores into the carpel 

 and enters the developing seed, where it tunnels and feeds 

 until fully grown. Before pupation, however, it makes its 

 way to the circumference of the cotyledon just within the 

 seed-coat (testa) where it pupates. Thence in due time 

 the beetle emerges, though in several species of this group 

 it may remain resting there for several months before it 

 bites its way through the skin in preparation for egg-laying 

 on the blossoms of the succeeding spring. 



In many cases the objects within which insect larvae 

 feed are the living bodies of other insects or of some larger 

 animal at whose expense they carry on their parasitic 

 existence. The modes of behaviour of insect parasites are 

 as remarkable as their structure, and often have a definite 

 bearing on the later stages of their own life-histories. As 

 an example we may sketch briefly the wanderings of the 

 maggots of the Warble-flies (Hypoderma) through the 

 bodies of the cattle wherein they live. The female flies lay 

 their eggs on the hairs of the legs or the lower parts of the 

 bodies of grazing cattle. Immediately after hatching the 

 tiny maggots crawl along the hair and bore into the skin. 

 Once beneath the skin they work their way upwards, their 

 behaviour suggesting that they have the " negatively 

 geo tropic " reaction. But their migrations are too com- 



