I 



THE HYMENOPTERA. 1 87 



and which, like men in armour, care little for the attacks of their 

 fellows, succumb to the active lancer-like parasitic flies. The 

 weevils, for instance, are long-lived insects, and are encased in 

 armour, but their active enemy finds out the joints, and sticks in 

 its ovipositor between the articulations of the body, and lays the 

 egg, which grows like a canker within. 



The parasitic Hymenoptera are of all dimensions ; many are of 

 considerable size, but the name of the minute insects is indeed 

 legion. So small are some of their larvae that several can be 

 accommodated within the body of an Aphis or plant louse, and 

 even in an egg of an insect. The eggs of many Lepidoptera are 

 destroyed by the larvae of the parasitic Hymenoptera that have 

 become developed within them from the eggs introduced by the 

 ovipositor. 



Almost all these parasites introduce their eggs under the skin 

 of their victims, so that their larvae are never seen, but there are 

 some kinds which only lay their eggs on the outside of caterpillars, 

 and other insects. When the larvae of these last-mentioned para- 

 sites are hatched they pinch up the skin with their mandibles, 

 and force the front part of their heads within the victim's body, 

 and remain in that position. They then suck the juices of their 

 prey, and the greater part of their body is exposed to the air. 



Since nearly all the parasitic Hymenoptera lead the same sort 

 of life, we might expect not to find any great structural difi"erences 

 amongst them. There is, however, a considerable variety in the 

 length of the ovipositor of the females. The females which deposit 

 their eggs within the bodies of caterpillars or larvae that live in the 

 open air have very small ovipositors ; those which attack larvae 

 which are underground, or are protected by some shelter, have longer 

 instruments ; and those that have toreach insects which live within 

 the trunks of trees, have very large and greatly developed egg 

 depositors ; so that the IcJinewnons habits and prey may be 

 guessed by the length of the ovipositor. 



Nature employs these parasites constantly when insect life is 

 too luxuriant ; they stop the multiplication of a crowd of creatures 

 that would do an infinitude of injury, and they limit the numbers and 

 the geographical distribution of many species. When the insects 

 which are most injurious to agriculturists are studied, the important 



