222 THE SOLITA RY WA SPS. 



are not killed outright, but rendered motionless; they are then 

 conveyed to a burrow previously formed by the Sphex, and, 

 continuing to live in their paralyzed condition for several 

 weeks are at last available as food for the larvae when there are 

 hatched. Of course the extraordinary fact which stands to be 

 explained is that of the precise anatomical, not to say also phy- 

 siological knowledge which appears to be displayed by the in- 

 sect in stinging only the nerve centers of its prey."* 



Before beginning any discussion of this remarkable instinct 

 it is most important that we have before us the facts that are to 

 be explained. Romanes depended upon Eabre for his knowl- 

 edge of the subject, and while Fabre is unquestionably the most 

 accurate of observers it does not necessarily follow that all of 

 his inferences must be accepted. "We have used the quotation 

 from Romanes because it represents the current opinion of 

 naturalists on the subject, and also because it presents the in- 

 stinct as dependent upon several matters of fact. The first 

 assertion, that the prey is stung in the chief nerve-centers is not 

 a matter of ascertained fact at all but an inference drawn from 

 the observation that some of the victims are not killed but only 

 paralyzed. The next step in the argument is a more or less 

 unconscious one, namely, that the wasp does not desire to kill 

 but means to paralyze. Then comes the assertion that the 

 prey remains motionless for several weeks. So far as we know 

 the facts relating to this point, they are as follows: Out of our 

 forty-five species of solitary wasps about one-third kill their prey 

 outright. Of tho-se that remain there is not a single species in 

 which the sting is given with invariable accuracy. To judge 

 from the results, they scarcely sting twice alike, since the vic- 

 tims 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 

 among the aculeate hymenoptera, live anywhere from two to 

 forty days. 



To take a rapid review of some of the genera, among the 



*The italics are ours. 



