io8 ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



The most interesting cases of the social habit are to be found 

 among Insects and Backboned Animals, which it will be well to 

 consider separately. 



SOCIAL INSECTS (!NSECTA) 



Some of the most remarkable facts in natural history have 

 been made known by those who have sUidied the complex com- 

 munities existing among various species of Membrane -Winged 

 Insects (Hymenoptera) and Net-winged Insects (Neuroptera). 

 The extent to which division of labour is carried varies greatly 

 in different cases, so that we are able to get some notion of the 

 successive stages which have marked the evolution of the social 

 habit. 



SOCIAL MEMBRANE- WINGED INSECTS (HYMENOPTERA). The 

 most salient point distinguishing highly organized communities of 

 Bees, Wasps, and Ants is the presence of a varying number of 

 "castes" or kinds of individual. In the Honey-Bee (Apis melli- 

 fica), for instance, a hive contains not only males (drones) and an 

 egg -producing female (queen), but also numerous "workers", 

 which are a second kind of female, having nothing to do with the 

 production of eggs, but, as their name indicates, labouring for the 

 benefit of the republic. And in other cases there may be more 

 than three castes, as we shall see in the sequel. Worker honey- 

 bees differ markedly in size and structure from the queen, as the 

 result of a long course of evolution, and it will be desirable to 

 begin with simpler communities, where such sharp distinctions do 

 not exist. 



BEES. Some account has already been given of Carpenter- 

 Bees, Mason- Bees, and Leaf-cutting Bees, solitary forms in which 

 the female not only lays eggs but also makes and stores a nest 

 (see vol. iii, p. 390). These and many other non-colonial insects 

 exhibit very elaborate adaptations to their surroundings, and it 

 would be a mistake to consider them as necessarily lower in the 

 scale than colonial forms, which have evolved on entirely different 

 lines. Here, as in all other cases, success in the struggle for 

 existence may be attained in widely different ways. 



From the purely solitary life led by the bees above-mentioned, 

 we pass to a curious case described by Fabre (from his observa- 

 tions in South France), where a certain amount of co-operation is 



