290 THE BRITISH NATURE BOOK 



are more than 2,000 species, many, such as the Currant Saw-fly and Pear 

 Saw-fly, being pests of garden and orchard. Some are about | inch across 

 the wings ; the Currant and Gooseberry Saw-flies being yellow, with black 

 head, antennae, and three short patches on the back. The larvae have twenty 

 legs. Many feed on leaves, others in galls. The pupa is in a silken cocoon, 

 generally buried in the ground. 



WOOD-WASPS 



(which, though like in general colouring, are not to be confused with the 

 true wasps) are represented in Great Britain by two species, not very common. 

 The Giant Wood-wasp (Sir ex gigas) looks a very formidable insect, with 

 its long and strong ovipositor, by which it inserts its eggs in the wood of 

 trees, in and on which the larvae feed. This wood-wasp is yellow, with two 

 black bands. The female is at once distinguished from the male by its egg- 

 laying instrument. It is quite harmless, as it possesses no sting. 



The Steel-blue Wasp (S. juvencus) is not so large, and the female has a 

 purple-blue abdomen, that of the male being yellow with a black apex. The 

 male has black antennae, and thus may be distinguished from the male of the 

 preceding, which has yellow antennae. 



The Gall-flies, of which we have three hundred species, are responsible 

 for the " oak-apples " and " bedeguars " and other strange excrescences upon 

 our trees. The female pierces the leaf or twig, and lays her egg within the 

 incision. This irritates and inflames the vegetable tissue, so that a swelling 

 takes place, forming the gall in which the larva lives. 



Sub-order ii. APOCRITA. 



The larva of all insects in this group is a white, legless grub, dependent 

 on provision made by its parent. 



ICHNEUMON FLIES. 



There are probably two thousand species at least in Great Britain. Some 

 lay their eggs in the bodies of caterpillars, upon which the larvae feed, in this 

 case performing a very useful task, for they destroy in this manner countless 

 numbers of butterflies and moths. 



Others attack wood-burrowing grubs, such as those of the Giant-tailed 

 Wasp, in which case they have a very long ovipositor, capable of boring 

 through the wood and reaching the grub below. The full-fed larvae leave the 

 body of their victim and spin cocoons, in which they pupate. 



The Ichneumon which preys upon the Giant-tailed Wasp is almost as 

 large an insect, black, with red legs, and two white spots on each segment 

 of the abdomen. Other species are very small. The typical Ichneumon 



