INSTINCT OF EENDERING VICTIMS INSENSIBLE. 243 



mother, instead of provisioning her cell once for all, 

 brings food to the young grub from day to day. 



This, however, is an exceptional case, and the mode 

 of life of the solitary wasps raises one of the most 

 interesting questions in connection with instinct. The 

 Ammophila, for instance, having built her cell, places 

 in it, as food for her young, the full-grown caterpillar of 

 a moth, Nootua segetum. Now, if the caterpillar were un- 

 injured, it would struggle to escape and almost inevit- 

 ably destroy the egg ; nor would it permit itself to be 

 eaten. On the other hand, if it were killed, it would 

 decay and soon become unfit for food. The wasp, however, 

 avoids both horns of this dilemma. Having found her 

 prey, she pierces with her sting the membrane between 

 the head and the first segment of the body, thus nearly 

 disabling the caterpillar, and then proceeds to inflict 

 eight more wounds between the followino; se";ments ; 

 lastly crushing the head, and thus completely paralyzing 

 her victim, but not actually killing it; so that it lies 

 helpless and motionless, but, though living, let us 

 hope insensible. M. Fabre, to whom we are indebted 

 for a most interesting and entertaining series of essays 

 on this group of insects, argues that this remarkable 

 instinct cannot have been gradually acquired. 



The spots selected are, he says, exactly those 

 occupied by the ganglia. No others among the in- 

 numerable points which might have been chosen would 

 have answered the purpose; not one wound is mis- 

 placed or without effect. M. Fabre truly observes that 

 chance offers no explanation.* Moreover, he unhesi- 



* In the case of other insects, such as Mutilla, Chrysis, Leucospis, 

 Anthrax, etc., which do not possess the instinct of paralyzing their 

 victims, the young feed on the chrysalis, which is normally without 

 power of movement. 



