Very little exact information exists as to the habits and life-histories of the species. Christ and Drewsen, forty or fifty years ago, recorded that _M. europaea_ lives in the nests of bees of the genus _Bombus_, and Hoffer has since made some observations on the natural history of the same species in South East Europe, where this _Mutilla_ is found in the nests of ten or eleven species of _Bombus_, being most abundant in those of _B. agrorum_ and _B. variabilis_; occasionally more individuals of _Mutilla_ than of bees may be found in a nest. He supposes that the egg of the _Mutilla_ is placed in the young larva of the _Bombus_, and hatches in about three days; the larva feeds inside the bee-larva, and when growth is completed a cocoon is spun in the interior of the pupa-case of the bee. When the perfect Insects emerge, the males leave the nest very speedily, but the females remain for some time feeding on the bees' honey. Females are usually produced in greater numbers than males. This account leaves {95}much to be desired. From the observations of Radoszkowsky it is clear that other species of Mutillides are by no means confined to the nests of _Bombus_ but live at the expense of Aculeate Hymenoptera of various groups. This naturalist asserts that the basal abdominal segment of the parasite resembles in form that of the species on which it preys. The apterous condition of the females of Mutillides and Thynnides is very anomalous in the Fossors; this sex being in the other families distinguished for activity and intelligence. The difference between the sexes is also highly remarkable. The males differ from the females by the possession of wings and by the structural characters we have mentioned, and also in a most striking manner in both colour and form; Burmeister, indeed, says that in South America—the metropolis of Mutillides—there is not a single species in which the males and females are alike in appearance; this difference becomes in some cases so extreme that the two sexes of one species have been described as Insects of different families. [Illustration: Fig. 38—_Mutilla stridula._ Europe. A, Male; B, female.]