A very minute species which has been introduced into this country, probably from Brazil or the West Indies, is the Horse Ant (Myrmica molesta). It is a very small brownish-yellow species, which seems to have been first observed in England in 1828. It takes up its abode in houses, frequently in the neighbourhood of the kitchen fireplace, and when it multiplies becomes such a pest as to render the house uninhabitable. Some of the metropolitan districts have been particularly infested.
Tribe II.—Entomophaga.
Most of the insects belonging to this tribe are parasitic on other insects. The larvæ are footless. There are seven families included in the Entomophaga.
Fig. 29.—Cynips Gallæ Tinctoriæ (Mag.)
Family 18, Cynipidæ.—This family includes most of the gall flies. The number of species is very considerable. Of the great majority the females pierce with their ovipositor the tissues of plants and trees, and there deposit their eggs, from which the larvæ are soon hatched. The irritation caused by this intrusion of a foreign body into the tissues produces the galls which are so commonly met with.
Fig. 30.—Smicra Sispes (Mag.)
The galls produced by different species of flies differ greatly in form and structure. Some of them are round and smooth, like fruits, such as the cherry gall of the oak leaves, produced by the puncture of Cynips quercus-foli.