THE ICHNEUMON FLIES. 399 



the female is enabled to drill holes into living timber for the purpose of depositing the eggs, 

 When they are hatched, the young grubs immediately begin to gnaw their way through the 

 wood, boring it in every direction, and making burrows of no mean size. Those of the present 

 species prefer fir and pine, and I have had specimens of the wood sent to me which have been 

 riddled by the grubs until they looked as if they had harbored a colony of the ship- worm. 

 The perfect insects often make their appearance in houses, the larvae having been concealed 

 in the timbers and rafters ; and I know of one case where a gentleman who had built a 

 wooden garden-house, was sadly annoyed by the multitudes of the Sirex which emerged 

 from the timber. In such cases the insects do not seem to attain their full dimensions, 

 but appear dwarfed and stunted. All wood-boring insects are, however, extremely variable 

 in size. 



The next group of the Terebrantia is called Entomophaga, or Insect-eaters, because the 

 greater number of them are parasitic upon other insects, just as the Saw-flies are parasitic upon 

 vegetables. In these insects the ovipositor is furnished with two delicate spiculse, and the 

 last segments of the abdomen are not formed into a telescope-like tube. 



The first family is that of the Cynipidse, or Gall insects, the creatures by whose means are 

 produced the well-known galls upon various trees, the so-called oak-apple being perhaps the 

 best known, and the Ink-gall (also found on the oak) the most valuable. These Galls are 

 formed by the deposition of an egg in the leaf, branch, stem, twig, or even root of the plant, 

 and its consequent growth. The well-known Bedeguar of the rose, with its soft mossy 

 envelope and delicate green color, relieved by bright pink, is caused by one of these insects 

 (Gynips rosce) ; and the celebrated Dead Sea-apples are nothing but galls formed by the 

 Cynips insdna. The spherical oak-galls, which contain a single insect, and are about the 

 size of a large marble, are closely allied to the true Ink-galls ; and if one of these objects 

 be cut with a knife, the action of the astringent juice upon the iron of the blade will produce a 

 kind of ink. The best galls are those which are gathered before the insect makes its escape, 

 as the astringent quality is then more powerful. 



The true Ichneumons, of which a specimen is given in the illustration, form a vast group 

 of insects, the Ichneumonidse alone numbering many more than a thousand described and 

 acknowledged species. In them the ovipositor is straight, and is employed in inserting the 

 eggs into the bodies of other insects, mostly in their larval state. In some cases, this slender 

 and apparently feeble instrument is able to pierce through solid wood, and is insinuated by a 

 movement exactly like that which is employed by a carpenter when using a bradawl. When 

 not engaged in this work, the ovipositor is protected by two slender sheaths that enclose it on 

 either side. 



Were it not for the Ichneumons, our fields and gardens would be hopelessly ravaged by 

 caterpillars and grubs of all kinds, for practical entomologists always find that when they 

 attempt to rear insects from the egg or the larval state, they must count upon losing a 

 very large percentage by the Ichneumons. 



Take, for examples, three or four caterpillars of the common white cabbage butterfly, 

 place them under water, and open the body from end to end. It will be found that, in 

 almost every case, the caterpillar bears the seeds of death within its body in the shape of tiny 

 white grubs, like very minute grains of rice. These creatures are the young of an Ichneumon- 

 fly (Microgaster glomerdtus), and retain their place within the caterpillar until the time for 

 it to change into the perfect form. They then simultaneously eat their way out of the skin, 

 spin a number of bright yellow silken cocoons, and in process of time change into tiny flies- 

 and set out on their destructive mission. The caterpillar never survives their attacks, and is 

 seldom able to move away from the spot whereon it happened to be when the Ichneumons 

 make their escape, the body being enveloped in their yellow cocoons. 



All the Ichneumon-flies may be distinguished by their fussy restless movements, as they 

 run up and down any object on which they may settle, and the continual quivering of their 

 antennae. The two lower figures in the illustration belong to this family, that on the left 

 showing an example of the long ovipositor with which several species are furnished, and the 

 other being given in order to show the wasp-like abdomen and the curled antennae. 



