LARGE CABBAGE BUTTERFLY. 189 
came to maturity as butterflies; the remaining 
fifteen (7. e. nearly two-thirds) were destroyed by 
the parasite. Now, if the present instance is to be 
taken as a fair average example of what usually 
oceurs, (and I see no reason why it may not,) we 
should have had this season, were it not for the 
ravages committed by the Microgaster, almost two- 
thirds more of this already very abundant butterfly 
than we now have. In the course of a few seasons, 
supposing no other ‘ preventive check’ to come in- 
to operation, the Cabbage Butterfly would increase 
in a kind of geometrical proportion ; our gardens 
would soon be absolutely devoured and laid waste 
by the caterpillars; and it would scarcely be possi- 
ble to walk abroad without being smothered by the 
winged insects. So greatly are we indebted to this 
apparently contemptible little parasite, (whose ope- 
rations are unheeded by all but naturalists, and of 
whose very existence the generality are perhaps 
scarcely aware,) for keeping down the increase of 
an insect, which would otherwise become a serious 
and alarming evil. 
“I may observe, that, though the Cabbage 
Butterflies did not come forth from the chrysalis 
till July 18th to 20th, the silken pupee of Micro- 
gaster produced swarms of the winged insects by 
the 12th, ready to go forth and commence their de- 
structive operations on fresh broods of caterpillars. 
“ The Cabbage Butterfly appeared to me to be 
