132 ZOOLOGY. 



then igniting it. It is also a good plan to frequently 

 tread or roll down the ant-hills which are thrown up, 

 as in this way they wiU be dispersed in the end. 

 Ants are of service in forestry, but scarcely in 

 agriculture. 



Family : Ichneumonidse (Ichneumon Flies). 



The species of ichneumon flies deviate in many 

 ways from one another, but they all have similar 

 habits and play a similar part in nature. They all 

 have a longer or shorter ovipositor, always surrounded 

 by two flaps, and serving for laying eggs in other 

 animals. Those which seek their prey in branches 

 and leaves generally possess a very short ovipositor 

 not obvious on cursory examination ; those which lay 

 their eggs in insects inhabiting crevices, e.g. wood 

 insects, are often provided with a very long ovipositor. 

 No colonies and, consequently, no workers. 



The female ichneumon fly generally lays her eggs 

 in the body of an insect larva, on which the ichneumon 

 larvae developed from these eggs feed, using up the 

 reserve matter stored up in the fat body (p. 92). 

 Caterpillars are most infested; then follow false 

 caterpillars, and then the larvae of weevils and leaf 

 beetles. The eggs of a few kinds are laid in pupse, 

 or even in the eggs of moths and butterflies. They 

 always select for this purpose those insects which 

 possess reserve material. The large kinds of ich- 

 neumon fly lay only a single egg in' one host, 

 especially if the latter is not of large size ; many of 

 the smaller ichneumons, on the other hand, lay many 

 eggs (Fig. 90) in one host, even up to a hundred or 

 more. A caterpillar containing ichneumon eggs does 

 not at first appear diflerent from other caterpillars, 

 except that a dark spot or patch usually indicates 

 where its body was pierced by the ovipositor of the 

 ichneumon fly. The parasite breathes while in the 



