It sometimes happens that the development of the young spiders has so far advanced at the time of the Ichneumon’s intrusion that the latter’s intention is frustrated, and its offspring, instead of devouring, are themselves devoured. Again, some few of the eggs in an infested cocoon occasionally escape the general destruction and reach the adult condition, but there can be no doubt that Ichneumons are largely instrumental in keeping down the numbers of most species of spiders. The perils which attend the Spider after leaving the cocoon are no less formidable, and much more numerous. The whole newly-hatched brood may be destroyed by a heavy rain-storm. If there is not a sufficient supply of food suitable to their feeble digestive powers they perish of inanition, or eat one another. This cannibalistic propensity is a considerable factor in the mortality among young spiders, and the adult animals frequently prey upon one another. _Argyrodes piraticum_, in California, invades the webs of larger spiders of the family Epeiridae, which it seizes and devours. _A. trigonum_, common in the eastern states of North America, has the same habit.[288] Hentz found in Alabama a spider, which he named _Mimetus interfector_, of still more ferocious and piratical habits. Its special quarry is _Theridion tepidariorum_. Sometimes the _Theridion_ overcomes the invader, and one case was observed in which a second _Mimetus_ was devouring a _Theridion_ beside the dead body of its predecessor, who had come off the worse in the combat. The eggs of _Theridion tepidariorum_ are also sometimes devoured by this spider, and a similar propensity has been observed in some English species, for Staveley[289] states that it is common to see certain spiders of the genus _Clubiona_ feeding upon the eggs which have been laid by their neighbours. The larvae of some Hymenopterous insects are parasitic upon Spiders themselves, and not upon their eggs. Blackwall found this to be the case with the larvae of _Polysphincta carbonaria_, an Ichneumon which selects spiders of the genera _Epeira_ and _Linyphia_ on which to deposit its eggs.[290] The spider thus infested does not moult, and is soon destroyed by the parasite which it is unable to dislodge from its back. Menge, in his _Preussische Spinnen_, enumerates several cases of parasitism in which the larva, as soon as it has developed from the egg, enters the spider’s body, there to continue its growth. Spiders are also subject to the attack of a parasitic worm, _Gordius_ (cf. vol. ii. p. 173).