The American “blue digger wasp” (_Chlorion caeruleum_) excavates its nest in the ground, and inserts a single large spider of any species.[293] Another wasp, of the genus _Elis_, selects the Wolf-spiders, and especially _Lycosa tigrina_, for the use of its larvae, while _Priocnemus pomilius_ shows a preference for the Crab-spiders, or Thomisidae. One of the most remarkable instances is that of _Pepsis formosa_, which preys upon the gigantic spider _Eurypelma hentzii_, wrongly styled in America the “tarantula,” but really belonging to an entirely different family, the Aviculariidae. Fabre’s most interesting researches have established the fact that the instinct of the wasp leads it to sting the spider in a particular spot, so as to pierce the nerve-ganglion in the thorax. The precision with which this is effected is absolutely necessary for the purpose of the insect. If stung elsewhere, the spider is either incompletely paralysed, or it is killed outright, and thus rendered useless as food for the future larvae of the wasp. On the one hand, therefore, the Tarantula has acquired the habit of striking the wasp in the only point where its blow is instantaneously fatal, while on the other the wasp, with a different object in view, has been led to select the precise spot where its sting will disable without immediately destroying the spider. The latter case is, if anything, the more extraordinary, as the insect can hardly have any recollection of its larval tastes, and yet it stores up for progeny, which it will never see, food which is entirely abhorrent to itself in its imago state. Spiders taken from the egg-nests of wasps by M‘Cook survived, on the average, about a fortnight, during which period they remained entirely motionless, and would retain any attitude in which they were placed.