ch the wasp has closed up the
hole that contains her grub, until the tip of the ovipositor reaches the
soft body of the insect. Into this it pierces, and deposits an egg, and
is withdrawn. The slight puncture is scarcely felt by the grub, which
continues to eat and grow; the inserted egg, however, presently hatches,
and produces the ichneumon-grub, which begins to feed on the fat of the
wasp-grub, instinctively avoiding the vital parts, until the latter has
attained nearly its full size, and is ready to pass into the pupa state;
when, its vigour being gone, it fails to accomplish the metamorphosis,
the insidious intruder, now also full grown, taking its place, and by
and by issuing from the hole a perfect Ichneumon.

How often has the enthusiastic young entomologist been subjected to sore
disappointment by the parasitic habits of these _Ichneumonidae_! He has
obtained some fine caterpillar, a great rarity, and by dint of much
searching of his Westwood or his Stainton, feels quite certain that it
is the larva of some much-prized butterfly. He ascertains its leaf-food;
which it eats promisingly; all goes on encouragingly. Surely it cannot
be far from the pupa state now! When some morning he is horrified to
behold, instead of the chrysalis, a host of filthy little grubs eating
their way out of the skin of his beautiful caterpillar, or covering its
remains with their tiny yellow cocoons.

Some of these parasites are so minute that their young are hatched and
reared in the _eggs_ of other insects. Bonnet found that the egg of a
butterfly, itself no bigger than the head of a minikin pin, was
inhabited by several of the stranger grubs; for out of twenty such eggs,
he says, "a prodigious quantity" of the grubs were evolved.

A very interesting tribe of insects, so diverse from all other known
forms as to constitute an order among themselves, that of the
_Strepsiptera_, passes its youth in the bodies of certain wild bees. Mr
Kirby's account of his first detection of one of these, though often
quoted, is so interesting that I must cite it afresh. "I had previously
observed," he remarks, "upon bees something that I took to be a kind of
mite (_Acarus_), which appeared to be immovably fixed just at the
inosculations of the dorsal segments of the abdomen. At length, finding
three or four upon an _Andraena nigroaenea_, I determined not to lose the
opportunity of taking one off to examine and describe; but what was my
astonishment wh