Big fleas have little fleas
Upon their backs to bite ’em;
Little fleas have smaller fleas,
So on _ad infinitum_;
which is very true, inasmuch as from the great humble-bee down to
the tiniest corn-thrips—a mere speck of dust to the naked eye—all
insects have their parasites, and generally their own special species
of ichneumon, to prevent their over-increase and to preserve the due
balance of nature. There is a species of longicorn beetle, found
in Pennsylvania, which feeds upon the tender bark of young hickory
shoots. When laying-time arrives, the female, having deposited her eggs
in cavities perforated in the bark, carefully cuts a groove, about
one-tenth of an inch wide and deep, round the shoot just below where
her treasures lie. The object, or rather we suppose we ought to say
the consequence, of this act is the withering and decay of the shoot,
a provision for the sustenance of her young, which, when in their
larval state, live upon dead wood! This remarkable insect is called the
hickory girder from the above-mentioned habit, which, we think, is one
of the most extraordinary instances of foresight, through a mere blind
instinct, that have ever come under observation.
The gadfly (_Œustrus equi_), whose larvæ are the bots which inhabit
the intestines of the horse, gains for her progeny that comfortable
position by entrapping the animal itself into introducing her eggs
within its stomach. For this purpose, she lays her eggs upon such
portions of the horse’s body as he is in the habit of frequently
licking, such as the knees, shoulders, &c. The unerring nature of her
instinct is shown by the fact that she never chooses as a nidus any
portion of the body which the horse is unable to reach with its tongue.
Having thus been introduced into their natural feeding-grounds, the
bots there pass their larval existence, until, it becoming time for
them to assume the pupal form, they go forth with the animal’s dung
to reach the earth, burrow into it, and therein pass the insects’
purgatory.
Again, one of the grain-moths (_Gelechia cerealella_) shows remarkable
instinct in adapting itself to circumstances according to the time of
year when it has to deposit its eggs. The first generation of these
moths, emerging in May from pupæ which have lain in the granaries
through the winter, lay their countless eggs upon the as yet ungathered
corn, upon which their young play havoc until, having passed through
the necessary stages, they come out in the autumn as the second
generation amidst the now stored-up grain. Now, however, their instinct
prompts them, not, like the first generation, to go forth to the fields
to seek the proper nest and future nourishment of their young, but
bids them deposit their eggs upon the store of wheat ready at hand.
Thus, two following generations of the same insect are led by their
instincts to different habits to suit the altered and, in the last
case, unnatural position of their infants’ destined food-supply.
The interesting mason-wasp, having with great care and skill bored
out a cylindrical hole in some sunny sandbank, deposits at the bottom
of this refuge her eggs. Next, provident mother as she is, she seeks
out about a dozen small caterpillars, always of the same species, and
immures them alive in the pit, as food for her cruel children. In
making her selection of grubs to be thus buried alive, she rejects any
that may not have reached maturity; not, we imagine, upon the score of
their not being so full-flavoured, but because, when not full grown,
they require food to keep them alive; whereas, when of mature age, they
will live a long time without nourishment, ready to turn to chrysalides
when opportunity occurs.
These are but a few of the instances which might be adduced in
illustration of this foresight in insects, which compensates for
their not being allowed in person to superintend the welfare of their
offspring. In many cases, it would be better for human progeny were
their parents thus endowed with an unerring instinct, rather than with
an uncertain will.