226 DISEASES OF INSECTS. 
Ichneumonidan devourers. These in some cases are so 
numerous as to destroy the tithe of the kinds they at- 
tack". Thus an ever-watchful Providence prevents 
these parasites from becoming so numerous as to anni- 
hilate in any place the species necessary for the mainte- 
nance of the general economy and proportion of animal 
and vegetable productions. Amongst the assailants of 
the Hymenoptera, none seem to have a more laborious 
task assigned them than those that pierce the various 
galls in which the larvae of the Cynips tribe are inclosed. 
To look at an oak-apple, we should think it a work of 
difficulty, requiring much sagacity and address, for one 
of our little flies to discover the several chambers lurk- 
ing in its womb, and to direct their ovipositor to each 
of them. Its Creator, however, has enabled it instinc- 
tively to discover this, and furnished it with an appro- 
priate elongated instrument, which will open a way to 
the deep and hidden cells in which the grubs reside, 
penetrate their bodies, and to each commit an egg. 
When it prepares to perforate the gall, the Ichneumon 
begins by depressing this organ, that it may extricate it 
from its sheath ; it next elevates its body as high as pos- 
sible, and bending the instrument till it becomes per- 
pendicular to th^e body and to the gall, so as to touch 
the latter with its point, it then gradually plunges it in, 
till it is quite buried b . A very remarkable Hymenopte- 
rous parasite {Lcucospis), which when unemployed turns 
its ovipositor over the back of its abdomen, so that its 
end points to its head, is said to deposit its eggs in the 
nest of the mason-bee, most probably in the larva : but 
the curious observations that are stated to have been 
» Reaum. ii. 454 — . h De Geer ii. 879 — . 
