SOLITARY AND SOCIAL WASPS 



nest had been cast. Such a block when dusted over with 

 sand was accepted by the wasp, and had the advantage over 

 the real nest that its contents could be examined without 

 doing much damage to the site. 



After making the nest, the female catches a caterpillar, 

 stings it until it is paralysed, drags it into the nest, and lays 

 an egg on it. The nest is closed, and opened again only 

 after some days when the wasp-grub will have hatched and 

 may need a second caterpillar. Adlerz in Sweden had sug- 

 gested that each female might be able to look after more 

 than one nest at the same time, and this Baerends found to be 

 true. Sometimes as many as three nests were kept going, 

 each in a different stage and needing different treatment. In 

 one the egg might not have hatched, in the second the grub 

 might need more food, whereas the third might be ready for 

 final closure. The female at first sight gives the impression 

 of knowing what treatment each nest requires, but experi- 

 ment showed that the " knowledge " was of a very primitive 

 type. Normally, the wasp makes a morning inspection of the 

 nests and this determines how she treats each one for the rest 

 of the day. Thus if on the first inspection she finds a nest 

 needs food, food is put into it even if a caterpillar has already 

 been placed experimentally in the nest. She seems to be 

 unable to revise her first impression until another twenty- 

 four hours have passed. Nevertheless the successful accom- 

 plishment of several elaborate duty-sequences within one 

 day, together with her marked ability in finding her way 

 about, make this wasp one of the most gifted of the solitary 

 species. 



THE VARIETIES OF WASP 



In Britain the word " wasp " is usually applied to one of 

 the common social species which eat fruit and sometimes 



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