372 CHARACTERS OF INVERTEBRATE ANIMALS 



though to this there are many exceptions. The abdomen is 

 stalked, and the female is provided with a piercing ovipositor by 

 which punctures are made for the reception of eggs. The larvae 

 are pale legless grubs. It is stated as probable that the sub- 

 order contains 20,000 species or even more, which means an 

 innumerable host of enemies to other insects. The Winter Moth 

 {Cheimatobia brumata), for example, is attacked by no less than 

 63 different kinds of Hymenoptera belonging to this group. Two 

 leading families are the Gall- Flies and Ichneumon- Flies. 



Ga[l-Flies are so named because they puncture plants for 

 egg-laying purposes, with the result that the wounded parts give 

 rise to those peculiar excrescences known as " galls ", of which 

 the spherical brown bodies called " King Charles's oak-apples ", 

 common on the oak, are known to everyone who has been in 

 the country. This tree indeed is peculiarly liable to the attacks 

 of different species of gall-fly, which lead to the production of 

 galls of totally different appearance, some resembling currants, 

 others looking like little cones, and others again being in the form 

 of circular scales (" oak spangles ") on the backs of the leaves. 



We may mention, as a specific example of a gall-fly, the form 

 Rhodites roses, which is responsible for the tufted red galls often 

 seen on wild rose-trees and known as rose-bedeguars or " old 

 man's beard ". 



Ichneumon- Flies constitute a family of which nearly 6000 species 

 have been described, over 1200 of these being British. The 

 larvae usually attack caterpillars, in or on which the eggs were 

 laid by the parent. Insects of other kinds, and even spiders, are, 

 however, attacked by some of the species. It was till recently 

 thought that the parasite subsisted by devouring the non-vital 

 parts of its host, but it is more probable that it simply absorbs 

 the blood of the caterpillar through its skin. 



One common ichneumon - fly [Microgaster glomeratus) lays 

 its eggs in the caterpillar of the common white Cabbage Butterfly, 

 within which they hatch out. When the unfortunate host has 

 reached its full term of growth, and should be ready to turn into 

 a chrysalis, it is too much enfeebled to do so. The unwelcome 

 guests now bite their way out of the caterpillar and become pupae 

 on their own account, and it is no uncommon thing to find a dead 

 caterpillar which has fallen a victim to ichneumon larvae side by 

 side with a little heap of pupae belonging to these foes. Another 



