1903 Ichneumons 149 



adipose tissues of the caterpillar's body. Vital organs are 

 by instinct avoided, since the destruction of these would be 

 also fatal to the parasite in its earlier stages : those parts 

 which go to sustain the caterpillar during its pupal existence 

 are gradually sapped, and it is not till, or till just before, it 

 becomes a chrysalis that the host is destroyed, for then the 

 grub, finding itself full-fed, has no further need of its living 

 pabulum. Within the dead pupa- case the parasite spins for 

 itself a silken cocoon, and, when you are looking for the 

 moth's emergence, issues forth in full perfection of wing and 

 leg to perpetuate its good work in the balance of Nature. 

 The intruder does not, however, always have it all its own 

 way, for in many instances there are what are known as 

 hyperparasites : these are species which prey upon the 

 parasites, and are sometimes very closely related with them. 

 In one instance I have found even the hyperparasite de- 

 stroyed by yet another entomophagous grub, so that, in this 

 case, the poor caterpillar was actually carrying about three 

 living grubs, each within the other, in her own body ! How 

 much farther the process may be carried I cannot conceive, 

 but enough has been said, I think, to prove that " There are 

 more things in heaven and earth, Horatio, ..." 



The economy of the Ichneumonidae is more or less an- 

 alogous in every case ; and every schoolboy who essays to 

 breed Currant Moths has expressed disgust in more or less 

 forcible terms at the appearance of Ichneumon trilineatus. 

 Some kinds lay but a single egg in each caterpillar, some lay 

 several ; the host's pupa is often used as a protection for 

 their own, but many kinds construct free cocoons, which, in 

 certain cases, are attached for safety to a twig by a long and 

 slender filament, while others are buried in the ground or in 

 moss. What will strike the observer is the extreme similarity 

 of the grubs of every species, pointing to a low state of 

 specialisation, which to a lesser extent is perpetuated in the 

 imagines. 



And here we come to the real difficulty connected with 

 these insects — their maddening family likeness. So great is 

 this that the merest lay mind knows an Ichneumon when he 

 sees one, but only a specialist can tell to what species it 

 belongs. In the days of the old entomologists — Ray, 



