27 
that this exemption does not exist; for though I 
have not myself been so fortunate as to find any 
species of ichneumon in their nests, one has been 
seen by Mr. Denison in several instances, and ob- 
served in all the stages of its growth. It is described 
by him as a fly as large, or nearly so, as the wasp 
itself: the head and forepart of the body black: the 
abdomen yellow, with a dark streak down the back : 
legs and under wings black: upper wings dusky. 
This fly deposits its egg upon the grub of the wasp 
at the moment it assumes the pupa: as soon as the 
egg is hatched, it devours the grub of the wasp en- 
tirely, and itself assumes the pupa and imago form 
in the cell of the wasp. As it is always found in 
cells closed up by the grub of the wasp in order to 
the assumption of the pupa state, it is probable that 
the parent fly may pierce the covering of the grub 
with its ovipositor, and lay its egg in that manner, 
the hole made in the covering being so small as to 
escape notice. These flies are most likely to be 
found where single cells are seen closed, after the 
inhabitants of the adjacent ones have quitted them ; 
because the ichneumon has to go through three 
stages, while the wasp has only to pass the pupa 
state, supposing the grubs in the same layer to be 
nearly of an age at the time they were deposited. 
I am not aware that the existence of this ichneumon 
has ever been mentioned by any writer on ento- 
mology, nor was any other described till some time 
after this one had been observed by Mr. Denison ; 
but a similar discovery has since been made by Mr. 
Wood of Manchester, who observes, “ In examining 
“ the combs of some wasps’ nests, in one of them I 
“discovered many cells, about half the length of 
