DISEASES OF INSECTS. 219 
their length, emulate the giants amongst insects. The 
former, unless appropriated to the eggs themselves, usu- 
ally commit many eggs to a single larva, while the latter 
are directed by their instinct to introduce into them only 
one. Some of the former description are endowed with 
the faculty of leaping a . The food of Ichneumons, and 
indeed of other internal parasites, is chiefly the epiploon 
or fat of the larva, but they never touch any vital organ ; 
so that it continues to feed, and probably more voraci- 
ously, grow, cast its skin, and often it changes to a chry- 
salis, although at the same time inhabited by an army of 
these little devourers. 
Ichneumons, as far as has been at present ascertained, 
are parasitic upon other insects chiefly in their three first 
states, a solitary instance only having been observed of 
their inhabiting an imago ; but from their first exclusion 
as eggs from the ovary till their assumption of that state 
they give them no rest. I shall therefore first treat of 
those that infest the eggs; next those appropriated to 
larva; and lastly those that devour pupce. 
Vallisnieri appears to have been the first naturalist 
who discovered that Ichneumons were appropriated to 
the eggs of other insects. He observed one proceed 
from those of the emperor-moth {Saturnia Spini) : find- 
ing two holes in each egg, one larger than the other, he 
conjectured that one was made when it entered, and the 
other when it emerged. In this case the egg of the 
Ichneumon must be fixed on the outside of the egg it 
2 De Geer i. 608. Linne has made a mistake with regard to the 
Ichneumon here alluded to, in calling De Geer's saltatorious Ichneu- 
mon /. Muscarum, and referring for it to t. xxxii./. ID, 20 of that 
author ; whereas the Ichneumon that preys upon the aphidivorous 
flies does not jump, and is figured by De Geer 605. t. xxxiv./. 26 — 
29. The jumping one feeds on the larva of a Coccinclla. 
