132 THE EVOLUTION OF INSTINCT 



untouched, and no malaxation was practised. In the 

 second seven stings again, but given in the anterior and 

 middle segments, followed by slight malaxation. In the 

 third only one sting was given, but the malaxation was 

 prolonged and severe." The severity of the stinging as 

 indicated by the conditions of the caterpillars stored in the 

 nest also varies. Of fifteen caterpillars which were stung 

 by Ammophila urnaria the Peckhams found that " some of 

 them lived only three days, others a little longer, while 

 still others showed signs of life at the end of two weeks. " 

 And in summing up their observations on the stinging in- 

 stinct these writers state that "out of forty-five species of 

 our solitary wasps about one-third kill their prey outright. 

 Of those that remain there is not a single species in which 

 the sting is given with invariable accuracy. To judge from 

 results they scarcely sting twice alike, since the victims of 

 the same wasp may be killed at once or may live from one 

 day to six weeks, or perhaps ultimately recover. Even the 

 caterpillars of Ammophila, the most distinguished surgeon, 

 live anywhere from two to forty days." 



Contrary to the conclusions of Fabre, who contended that 

 the instincts of Ammophila are practically undeviating, the 

 Peckhams remark that "the one preeminent, unmistakable 

 and ever present fact is variability. Variability in every 

 particular in the shape of the nest and the manner of dig- 

 ging it, in the condition of the nest (whether closed or open) 

 when left temporarily, in the method of stinging the prey, 

 in the degree of malaxation, in the manner of carrying the 

 victim, in the way of closing the nest, and last, and most 

 important of all, in the condition produced in the victims by 

 stinging." 



Among certain species of ants, Polyergus rufescens and 

 several species of Formica and Lasius, whose Iarva3 ordinarily 



