Fabre's observations on allied species of Diptera render it, however, highly probable that the destruction is effected by the young fly-larva and not by the mother-fly. Mr. R. C. L. Perkins once observed several individuals of our British _O. callosus_ forming their nests in a clay bank, and provisioning them with larvae, nearly all of which were parasitised, and that to such an extent as to be evident both to the eye and the touch. In a few days after the wasps' eggs were laid, swarms of the minute parasites emerged and left no food for the _Odynerus_. Curiously, as it would seem, certain of the parasitised and stored-up larvae attempted (as parasitised larvae not infrequently do), to pupate. From which, as Mr. Perkins remarks, we may infer that (owing to distortion) the act of paralysing by the wasp had been ineffectual. Mr. Perkins has also observed that some of the numerous species of Hawaiian _Odynerus_ make a single mud-cell, very like the pot of an _Eumenes_, but cylindrical instead of spherical. This little vessel is often placed in a leaf that a spider curls up; young molluscs of the genus _Achatinella_ also {77}avail themselves of this shelter, so that a curious colony is formed, consisting of the _Odynerus_ in its pot, of masses of the young spiders, and of the little molluscs. Horne has recorded that the East Indian _O. punctum_ is fond of availing itself of holes in door-posts where large screws have been; after the hole has been filled with provisions, the orifice is covered over level with the surface of the wood so that it eludes human observation. It is nevertheless discovered by an Ichneumon-fly which pierces the covering with its ovipositor and deposits an egg within. The genus _Abispa_ is peculiar to Australia and includes some very fine solitary wasps, having somewhat the appearance of very large _Odynerus_: these Insects construct a beautiful nest with a projecting funnel-shaped entrance, and of so large a size that it might pass for the habitation of a colony of social wasps; it appears, however, that this large nest is really formed by a single female. The species of the genus _Rhygchium_ are also of insecticide habits, and appear to prefer the stems of pithy plants as the nidus for the development of the generation that is to follow them. Lichtenstein says that a female of the European _R. oculatum_ forms fifteen to twenty cells in such a situation, and destroys 150 to 200 caterpillars, and he suggests that, as it is easy to encourage these wasps to nest in a suitable spot, we should utilise them to free our gardens from caterpillars, as we do cats to clear the mice from our apartments.