56 Mr. W. E. Shuckarcl on the Habits 



their prey, an opinion however that I cannot coincide in for reasons 

 which I shall presently state. In the genus Pornpilus, some, as the 

 P. bifasciatus of Fabricius and the P. petiolatus of Van der Linden, 

 are simple in the tarsi and posterior tibiae ; but I suspect they nidifi- 

 cate in wood. Tlie black species of Psen, as I have observed, nidifi- 

 cate in wood, although their tarsi and tibiae are simple ; hence the 

 species of this genus cannot be placed in the class of Parasites. 

 With respect to Trypoxylon, I think there can be no doubt as to its 

 being a parasite, as it is a very common insect, and constant oppor- 

 tunities occur for detecting it with its prey, were it predatory. In 

 the genus Pcmphredon,! suspect that only P. insignis is parasitic, — the 

 majority of them nidificate in wood ; but the P. minutus I have taken 

 only in sand, and as its anterior tarsi are simple, although the pos- 

 terior tibia; are spinose, it may possibly be a parasite ; but future 

 observation will determine this point, as well as decide which may 

 be treated as parasites among the sand-burro wers in general. But 

 I think we may entertain little doubt as to the genera Ceropales, 

 DoUchiirus, and Nysson being assignable to that class, and Gorytes 

 mystaceiis is, I have no doubt, also a parasite, and has thus acquired 

 a certain degree of celebrity by suggesting this discovery. Those 

 which I have not named are all true Fossores, taking them as they 

 appear in the published lists. 



With respect to St. Fargeau's auxiliary character, the spines of 

 the hinder tibiae, which he considers as assisting the insect in con- 

 veying its prey, I have already indicated that I do not subscribe to, 

 and for the following reasons : they are invariably placed on the 

 outside of the limb, and the insect in carrying its burthen would 

 necessarily clasp it with the inside ; exclusively of the fact of my 

 knowing only one genus that uses its posterior legs for this purpose. 

 Were this, therefore, their sole use, it would be derived merely from 

 the strength they might add to the member ; but I conceive their chief 

 importance is to assist the insect in buiTowing, for although some 

 species convey the particles of sand or earth out of their burrow 

 by their mouth, and pile them at its entrance for the purpose of 

 closing it after having dejjosited their progeny Avithin, to secure them 

 from the ingress of ants or their parasites (Note 4.), yet many 

 species burrow like a fox, tossing the sand out behind them with 

 their posterior legs ; and in the same way those which nidificate in 

 wood pass the particles beneath them, and eject them behind by means 

 of the spines with which their tibiae are armed, which fact I have 

 frequently observed while watching the habits of Crabro cephalotes. 

 Besides the evidently ill-adapted position of the spines for aiding 

 the insect in carrying, I have noticed the genus Oxybelus alone, to. 



