INSECT USURPERS. 477 



in eacli burrow, placing a single egg in every cell, and accom- 

 panying it with spiders, more or less in number according to 

 their size. 



One small species, Trypoxylon alternatum, may often be 

 found in the dead and broken stems of roses and brambles, the 

 insect boring away the soft pith and constructing a series of 

 cells, each separated from its neighbour by a wall of sand. The 

 cells are stocked with small spiders, and if the stem be carefully 

 cut open, the cocoons may be seen all in a row, each cocoon 

 filling as exactly as possible the cell in which the larva has 

 been reared. 



Whatever may be the case with the British species, it is 

 evident that some of the foreign Trypoxylons are parasitic upon 

 other insects, or at all events that they take possession of their 

 nests iu order to avoid the trouble of making burrows for them- 

 selves. The reader will remember that in the account of Para- 

 pison rufipcs Mr. Home mentioned that he had bred from it 

 specimens of Trypoxylon intrudens. The same observer states 

 that although Trypoxylon rejector builds cells of its own, it is 

 in the habit of appropriating those of other insects. In Plate 

 VIII. the elongated cells in the nests of the illustration are 

 those of the Trypoxylon. This is Mr. Home's account of the 

 insect as given in the Transactions of the Zoological Society, 

 vol. vii. part 3 : — 



" This curious little insect, when first hatched from the deli- 

 cate little Serpularia-like cells, was taken by me for some para- 

 site allied to the Ichneumoniclse, in consequence of my having 

 often observed it hovering at the mouths of the cells of the 

 smaller cell-building insects in my verandah. I found, how- 

 ever, that it brought mud and worked for itself, as well as 

 appropriated the cells of other insects which it found ready 

 to its hand. 



" I have nowhere found recorded its habits ; but I think I 

 have seen it carrying minute green spiders wherewith to fill its 

 cells. It certainly does not feed its young, but stores food ; for 

 it closes its cells directly they are ready, which none of the 

 Vespidre do. 



"The construction of these is very curious ; and the pellets 

 of earth used appear of a sandy character, which gives to the 

 structure great delicacy and fragility. At the same time the 



