Insects and their world 



the fact that in certain years outbreaks may occur of some species of 

 insects which previously had been virtually unknown. 



Some inseas live in communities of more modest size, which remain 

 the same, without great seasonal fluctuations in numbers. These often 

 occur where the breeding habits of the insects restrict them to situations 

 that are hmited in extent. Fleas, for example, breed in debris round the 

 living- or sleeping-quarters of the animal host. The larvae of the fleas 

 feed on scraps from the skin of the host, and mainly on the droppings 

 of the adult fleas, which contain undigested blood. Consequently fleas 

 are parasites of animals (mammals and birds) that have a den or nest, 

 and they live in a community there with the adult fleas riding about on 

 the host animal, but coming back frequently to the community-site. 



Ant-lions (Order Neuroptera, family Myrmeleontidae, Fig. 26) have 

 a fiercely carnivorous larva which lives at the bottom of a conical pit in 

 fine sand or dust (Wheeler called them 'Demons of the Dust'). Here 

 they He concealed until some insect wanders on to the steep slope of the 

 pit and begins to sHther down it. When the ant-lion hears — or feels the 

 vibration of — the grains of sand dislodged and falling down, it helps the 

 process by jerking its head and throwing sand at the prey until it falls to 

 the bottom, when it is seized and eaten. 



The community of ant-lions comes into being because only a few 

 places are suitable for the pits. The sand or dust must be very fine, and 

 quite dry, and the place must be sheltered from rain, otherwise the first 



Fig. 63. An exceptionally large chalcid, Hymenoptera-Parasitica 



94 



