THE SOCIAL INSECTS 



interfere with picnics. There are many other insects, includ- 

 ing even moths, with a similar black and yellow livery, 

 which are often mistaken for wasps and may indeed 

 gain some protective advantage if such mistakes are made 

 by birds. 



Entomologists, however, apply the word wasp in the broad 

 sense to several large groups of insects, many of which do 

 not show the black and yellow colours. The ichneumon 

 wasps, for instance, lay their eggs in or on other insects, 

 more rarely in spiders, and other animals. The act of laying 

 the egg seems to disturb the host very little, and it may 

 survive for a long time. But in the end, after the egg has 

 hatched, the ichneumon grub eats the entire contents of its 

 host, so that nothing but an empty skin is left. An insect 

 which does this is usually called a parasite; but it can just as 

 well be called a specialised predator which kills its prey at a 

 convenient moment. 



Solitary hunting wasps paralyse or kill their prey (which 

 may be a caterpillar, spider or something else of that sort) and 

 store it in a nest. Here again the prey is eaten by the grub 

 which hatches from the egg which the wasp has laid in the 

 nest. This type of behaviour is associated with a change in 

 the structure of the wasp's ovipositor: it becomes a sting. In 

 the ichneumon, the egg can be passed down between the 

 stylet-like blades of an ovipositor which thus acts like a 

 hypodermic syringe for injecting the egg into the host. In 

 the hunting wasp an egg pore is found at the base of sting ; 

 the ovipositor is then only a syringe for injecting poison 

 into the prey, or into any marauding enemies. A sting is 

 found in the nest-making ants, bees and wasps, though in 

 some of them it is not actually syringe-like. 



The solitary wasps themselves are a very large group 

 with a great diversity of appearance and habit. Some of 



