How insects behave 



The more advanced forms of social life are found in two Orders of 

 insects, Isoptera (termites) and Hymenoptera (bees, wasps, ants). These 

 two Orders are only distantly related in other ways, and their social 

 behaviour has been developed quite independently. It is all the more 

 remarkable that they have reached so many similarities, as a result of 

 convergence^ of which we shall have more to say in the following chapter. 

 There still remain profound differences between the two insect 

 'civilisations'. 



Let us consider first what features of social life the two Orders have 

 in common. They live in large colonies, with hundreds of thousands of 

 individuals, and they share the work of the nest by a division of labour 

 based on a system oi castes (Figs. 7, 9). Egg-laying is confined to fertile 

 females known as queens, of which there are few, or even only one per 

 nest. Fertile males are also few, and almost all the members of the nest 

 are sexually sterile, occupied exclusively with foraging for food, nest- 

 building, looking after young larvae or defending the nest against 

 attack. 



Which caste an individual belongs to is decided partly by whether 

 it developed from a fertilised egg or not, and partly by the food it re- 

 ceives during its larval life. Once it has become adult it does not change 

 caste. Members of different castes are different in appearance as well as 

 in behaviour. 



The chief difference between the social Hfe of the two Orders is that 

 in the termites the workers and soldiers may be sterile individuals of 

 either sex, whereas the workers of the social Hymenoptera are all 

 sterile females. In the Hymenoptera the males exist only for the nuptial 

 flight, and afterwards die or are killed off before the winter. In the ter- 

 mites one male remains fertile in the nest, and periodically re-fertilises 

 the female. 



Isoptera — Termites 



The termites, commonly known as 'white ants', fall into two bio- 

 logical groups. The dry- wood termites .burrow in wood above ground 

 level, and often cause wooden structures to collapse suddenly without 

 warning. The subterranean termites nest in the ground, but go on 

 extending the nest above ground level to produce the termitaria, or 

 'ant-hills' that are such a feature of tropical scenery. Some of the 

 biggest termitaria are to be seen in Australia, and may be 12-20 ft. high, 

 and 10 ft. in diameter. Inside they are a sponge-like mass of connecting 

 spaces, but the structure is of a very unsponge-like hardness, which 

 sometimes can be broken up only by explosives. 



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