In no manner is the mysterious influence of instinct over the insect
world more remarkably manifested than by the care taken by parent
insects for the future welfare of offspring which they are destined
never to behold. As the human parent upon his deathbed makes the best
provision he can for the sustenance and prosperity of his infant
children, whom death has decreed that he may not in person watch over,
so those insects which nature has decreed shall be always the parents
of orphan children, led by an unerring influence within, do their best
to provide for the wants of the coming generation.
The butterfly, after flitting through her short life, seeks out a spot
whereon to deposit her numerous eggs, not—as one might expect of a
creature devoid of mind—upon any chance plant, or even upon the plant
or flower from which she herself has been wont to draw her sustenance,
but upon the particular plant which forms the invariable food of the
larvæ of her species. The various kinds of clothes-moths penetrate into
our cupboards, drawers, and everywhere where furs, woollen garments,
&c., are stored, that they may there lay their eggs, to hatch into
the burrowing grubs which are the terror of our housekeepers. The
ichneumon tribe, one of nature’s greatest counterpoises to keep down
the too rapid increase of the insect world, lay their eggs in the larvæ
of other insects, which eggs when hatched develop into a devouring
brood, which ungratefully turn upon and devour the helpless creature
that sheltered them as a nest. The female ichneumon having discovered
a caterpillar or grub which her instinct informs her has not been
previously attacked, at once proceeds to thrust her ovipositor into the
writhing body of her victim, depositing one or more eggs, according
to the size of the living food-supply. When hatched, the larvæ devour
and live upon their foster-parent, avoiding in a marvellous way the
vital parts of their victim, whose life is most accurately timed to
last until its young tormentors are full grown, and not beyond. At one
time, we were led to believe in occasional instances of the instinct
of female ichneumons being at fault, by observing them apparently
ovipositing upon the dry shells of pupæ from which the butterflies
had escaped. This, however, we subsequently found to be an erroneous
idea, the fact of the matter being, that the caterpillar upon which the
parent ichneumon had laid her fatal egg, had had time, before the full
development of the young ichneumon grub, to turn to the pupal stage.
What, then, we saw was the young ichneumon fly just emerged from the
dry pupal case, the contents of which it had first devoured in its own
larval stage, then, itself turning to a pupa, it had lain, thus doubly
incased, until, having broken forth a perfect fly, it rested upon its
late prison, awaiting sufficient strength to come to its wings. What a
wooden horse of Troy such a chrysalis would prove, if introduced into
the breeding establishment of a collector!
Other members of the ichneumon tribe do not actually insert their eggs
into the destined food-supply of their young; but, as it were, going
deeper into calculation of future events, content themselves with
laying them in close proximity to the eggs of some member of the tribe
upon which it is their mission to prey.