SOCIAL PARASITES 



make slave-raids, but the young queen invades a Tetra- 

 morium nest and lives there without killing the host queen. 

 Both queens continue to lay eggs, but those of the host queen 

 produce thereafter nothing but workers, whereas the brood 

 of the parasite consists of all three castes but especially of 

 males and queens. The species is thus harmful to its host — 

 since it prevents normal reproduction — and degenerate, 

 because it is unable to rear its own brood. This is done for 

 it by the Tetramorium workers. In 1935 a new species of 

 Strongylognathus, S. diveri, was discovered by Diver, in 

 Dorset. It is very similar to S. testaceus, and probably has 

 similar habits. It certainly lives in the nests of Tetramorium, 

 and it has few and rather feeble workers. 



The third British parasitic ant is Anergates atratulus. It 

 too lives in the nests of Tetramorium. In England it has been 

 found only in the New Forest, and there only on very few 

 occasions. It is also rare on the continent. It is an example of a 

 group of rare species, each belonging to a different genus, 

 and probably showing the last stage in a long parasitic history. 

 Such forms are rare, it is thought, because they have passed 

 the point where parasitism is even a temporary advantage 

 and are now approaching extinction. 



Anergates has no workers. The male is wingless, of a pale 

 colour, and with a rather soft skeleton, more like a pupa than 

 an adult insect. The virgin queens are relatively small ; 

 after mating with their brothers in the colony which pro- 

 duced them, they fly off to try to invade new colonies. If 

 successful, they kill the host queen and begin laying eggs at 

 a great rate, their abdomen swelling to an enormous size. 

 The host workers care for the brood, but the whole colony 

 must die out rather quickly since the workers are no longer 

 being replaced. Although the species can live only in places 

 where Tetramorium colonies are numerous, it tends to reduce 



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