Mr. F. Smith on Wasps and their Habits. 393 



Mr. Walsh obtained five mud cells constructed by Agenia 

 bombycina, an American species ; they were " all alike, and 

 all of them found in company under the bark of the same 

 tree." From these five cells there hatched out, about the end 

 of June 1864, four specimens of Agenia and a single male 

 specimen of a species of Ceropales, a genus of Pompilida? : on 

 this evidence Mr. Walsh concludes the habit of parasitism to 

 be proved ; but to this I cannot assent. 



I have just alluded to Trypoxylon being reared from the 

 cells of Pison ; in that instance the cells were not deserted 

 ones, but fresh and stored with spiders. Now we know that 

 Trypoxylon is not a parasite, and we are therefore justified in 

 concluding that the insect found a cell built by Pison, in every 

 way adapted to its purposes, and took possession of it. I may 

 remark that the cells of Pison and those of Trypoxylon are 

 precisely of the same form and mode of construction. 



Mr. Home also bred Trypoxylon from a series of cells con- 

 structed by a solitary wasp, a new species of the genus Ptero- 

 chilus : these solitary wasps store their cells with caterpillars ; 

 therefore in this instance, as Trypoxylon stores up spiders, we 

 are led at once to the conclusion that the latter insect took 

 possession of the cells of the former. Such being the case, I 

 cannot see any reason why Ceropales may not in the same 

 way have taken possession of the cell of Agenia in the in- 

 stance mentioned by Mr. Walsh. 



I have remarked, in my observations on the genus Cero- 

 pales, in the ' Monograph of the Fossorial Hymenoptera :' — 

 " These insects have been considered parasites on the genus 

 Pompilus ; their legs almost destitute of spines, and the ab- 

 sence of cilia on the tarsi, I am inclined to consider indicative 

 of a peculiar economy." St. Fargeau considered them to be 

 parasitic insects ; and in the same class he placed all the 

 Fossorial Hymenoptera whose legs are destitute of spines : 

 this, however, was, in accordance with his theory, based en- 

 tirely on structure. Subsequent observation has long ago 

 proved his arrangement to be fallacious. Structure in some 

 classes of animals may prove a pretty correct index to habit, 

 but it fails to be so when applied to insects. There is no 

 family among the whole of those which constitute the fossorial 

 section more eminently fossorial in structure than the Scoliadae ; 

 their legs bristle with spines : yet these insects have long 

 ago been proved by Passerini to be parasites ; and when we 

 become acquainted with their habits, we see at once the 

 use of such a structure even in parasitic insects. Scoliaflavi- 

 frons has to burrow down to the cell of Oryctes nasicornis ; 

 and other species have been observed preying also upon 



