INSECT ECOLOGY 351 



determining the presence or absence of oviposition burrows of tiger 

 beetles, and the presence, absence, or number of eggs laid (Shelf ord) . 



Nutriment. The food of soil insects may be roots or stems of 

 lants, dead animal or vegetable matter, other insects or other animals. 

 Some insects are parasitic on burrowing mammals. Many ants derive 

 part of their nourishment from the root-sucking aphids or coccids 

 which they attend. Ants and termites sustain diverse relations as 

 regards food with various other insects and other arthropods that live 

 in their nests. Some species that burrow near the surface, as tiger 

 beetles and ant-lions, capture their prey from the surface of the ground. 



Soil that contains no organic matter, as pure quartz sand, is food 

 for no insect. Some larvae, as white grubs and wireworms, that subsist 

 primarily on roots of plants, can if necessary thrive for many months on 

 a diet of soil alone, but only because of the organic matter that it 

 contains. 



Interactions. The subject of interactions in the soil environment 

 can only be touched upon here. The character of the soil itself is 

 changed by the plants and animals that inhabit it. Thus burrowing 

 animals, as worms, crawfishes, insects, moles, mice, many larger 

 mammals, etc., alter the distribution and the physical and chemical 

 composition of the soil. Bacteria and fungi play important parts. 

 The soil is not fully effective in protecting its insect inhabitants from 

 predaceous and parasitic enemies among other insects, and soil insects 

 are themselves food for many birds, mammals, and other of the larger 



rimals. 

 2. ATMOSPHERE 

 LIGHT 



The most conspicuous effect of light is its directive effect on locomo- 

 tion. This phenomenon is discussed in another chapter (p. 306), 

 where it is shown that insects react either positively or negatively to 

 light, are often attuned to definite ranges of light intensity, and react 

 differently to light of different wave lengths. The results of photo- 

 tropism are often incidentally adaptive. As examples, the positive 

 reaction may take insects to their food, cause the nuptial flight of ants 

 or termites, or the swarming of bees; while the negative response may 

 lead insects into places of concealment, pupation, or hibernation. 

 Structures and functions are correlated with the presence or the absence 

 of light; for example, those of the eyes. Insects that live in darkness, 

 as boring species, subterranean forms, and cave insects, exhibit special 



