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 hr 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 
( Cynips rosoe ) ; and the celebrated Dead Sea-apples are nothing but galls formed by the 
Cynips instinct. 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 {Microg aster glomertitus ), 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 
antennse. 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 antennse. 
