J. H. Fabre pursued the study of the habits of fossorial wasps further. He ascertained that the captured insects were not dead, but only paralysed. The continuance of the function of certain organs demonstrated that the _Buprestes_, the weevils and other small creatures collected in the burrows of fossorial wasps, were alive. They could even perform some slight movements, but they were incapable of locomotion, and so could not escape. The mechanism of this paralysis, as far as could be ascertained by Fabre, is one of the most remarkable phenomena in nature. The fossorial wasps, guided by their instinct, immediately after having seized an insect or spider, bury their sting in the nervous centre which controls the movements of the legs. When animals with soft bodies, such as spiders and young crickets, are attacked, the operation does not present any difficulties. But Coleoptera in general, and the _Buprestes_ and weevils in particular, are furnished with a very hard covering which cannot be perforated by the small and slender sting of a fossorial wasp. To gain their object the wasps probe exactly between the first and second pair of legs in the median line of the under surface of the thorax. The skin is thinner at this spot, and they introduce their sting into the ganglia from which arise the nerves of the legs. In the case with the _Buprestes_ these ganglia are set close to one another, and a single prick suffices to affect the nervous centres of three pairs of legs. Once the sting has been inserted in this way the _Buprestis_ becomes paralysed, but lives for many days. “The _Cerceris_ which preys on Coleoptera,” writes Fabre,[35] “appears to have made its choice according to the dictates of an exact physiology and anatomy. It is impossible to see in its proceedings the results of happy chance; more than chance is required to explain adaptations so precise.” After having filled the burrow with a sufficient quantity of insects or spiders, fossorial wasps lay their eggs and carefully close up the entrance. In due course the larva is hatched, and devours the food that it finds close at hand. If the gathered insects were not paralysed, they could easily escape from their prison; if they were dead, putrefaction or desiccation (according to circumstances) would render them unfit for the larvæ. It is therefore sheer necessity that is the factor in the development of this marvellous instinct that induces the fossorial wasps to attack the nervous centres of their prey. When one insect has been devoured, the larva proceeds to another, and so on, until it is fully grown, whereupon it envelops itself in a case that protects it during the winter and following spring. In summer it changes at first into a chrysalis, and later into a perfect insect. It frees itself from the cocoon, takes to flight, and enters upon life like that of its mother, which it has never seen.