316 SUNDRY INSECTS 



On the minute island Lula, several colonies of very 

 hairy caterpillars, of the family Eupterotidae, were seen 

 on trunks of trees. Near one colony was a large Tachinid 

 fly, and the caterpillars, close together, seemed to be 

 aware of her presence, for they moved uneasily ; but 

 the fly moved as they moved, sidling about in a very 

 amusing manner so as always to face the caterpillars. 

 She endeavoured to find one that was not moving, 

 and then approached the head from in front. The long 

 hairs of the caterpillar projected from all parts except 

 the head, so as to form a chevaux de frise, but opposite 

 the head there was a small gap in the barrier. The fly, 

 having approached as close as she could, raised herself 

 up on her anterior legs and protruded forwards, beneath 

 herself, an enormous ovipositor whose tip projected in 

 front of her head. The egg was laid in a very brief instant 

 on or near the head of the caterpillar, but sometimes 

 the fly was unable to reach its head, and then had to 

 wait until the larva was near enough for her ovipositor 

 to reach between the long hairs so as to deposit an egg 

 on the flank of the larva. 



It was a most interesting and instructive proceeding, 

 illustrative of the adaptation of one enemy (the fly) to 

 meet a condition in its victim probably directed against 

 other enemies (birds). It was noted that the fly laid 

 its eggs fortuitously on any larva that presented itself, 

 so that one received many eggs but others none. This 

 might quite well lead to some of the offspring of the fly 

 receiving insufficient nourishment and being stunted in 

 growth or failing to develop. One sometimes meets the 

 opposite condition, when too few ova have been deposited, 

 and the parasites have not damaged the vital parts 

 of their host. I once reared a single Tachinid fly from 

 an Arctiid larva which eventually produced a perfect 

 moth ! 



Asilidae or Robber flies were often met with at the very 



