_Genera less skilful in the art of paralysing victims._--These researches show us that in the _Cerceris_ instinct is still subject to defect. In some neighbouring genera we can seize it, as it were, in process of formation. The way in which the _Bembex_, or Sand Wasp, provisions burrows by maternal foresight is much less mechanical than that of the _Sphex_. It is again Fabre who has described with most care the customs of this hymenopterous insect.[78] It hollows out for each egg a chamber communicating with the air by a gallery, and performs this work with little care and very roughly. Less skilful than the others, it does not amass at once all the provisions which its larvae will need during the period of evolution. When the offspring has absorbed the last prey brought, it is necessary to bring a new victim. This insect is scarcely more advanced than birds, who feed their young from day to day. And it is a great labour to re-open every time the gallery which leads to the nursery; on all these visits, in fact, the _Bembex_ fills it up on leaving, and causes the disappearance of all revealing traces. It is obliged to take so much trouble, because it has not inherited from its ancestors the receipt for the paralysing sting; it throws itself without care on its victim, delivers a few chance blows, and kills it. Necessarily it cannot, under these conditions, lay up provisions for the future; they would corrupt, and the larvae would not be benefited; hence the obligation of frequently returning to the nest, and of a perpetual hunt to feed descendants whom nature has gifted with an excellent appetite. According to the age of the offspring, the mother chooses prey of different sizes; at first she brings small Diptera; then, when it has grown, she captures for it large blow-flies, and lastly gadflies.[79] It will be seen, then, that if we suppose the instinct of the _Sphex_ to be slowly developed by being derived from a sting given at random, we make a supposition which is quite admissible and rests on ascertained facts. However this may be, the _Bembex_, returning to its burrow, is able to find it again with marvellous certainty, in spite of the care taken to hide it by removing every trace that might reveal its existence. It is guided by an extraordinary topographic instinct, which men not only do not possess, but cannot even understand the nature of. [78] _Souvenirs entomologiques_, 1879, pp. 225 _et seq._ [79] A Wasp found in La Plata, the _Monedula punctata_, as described by Hudson (_Naturalist in La Plata_, pp. 162-164), is an adroit fly-catcher, and thus supplies her grub with fresh food, carefully covering the mouth of the hole with loose earth after each visit; as many as six or seven freshly-killed insects may be found for the use of one grub.