Ch. 13: Nature's Night Lights - Page 2

their
insect enemies are not so squeamish, and devour them readily, just as
they also do the blister-fly, which one would imagine a morsel fitted to
disagree with any stomach. One of their enemies is the Monedula wasp;
another, a fly, of the rapacious Asilidas family; and this fly is also a
wasp in appearance, having a purple body and bright red wings, like a
Pepris, and this mimetic resemblance doubtless serves it as a protection
against birds. A majority of raptorial insects are, however, nocturnal,
and from all these enemies that go about under cover of night, the
firefly, as Kirby and Spence rightly conjectured, protects itself, or
rather is involuntarily protected, by means of its frequent flashing
light. We are thus forced to the conclusion that, while the common house
fly and many other diurnal insects spend a considerable portion of the
daylight in purely sportive exercises, the firefly, possessing in its
light a protection from nocturnal enemies, puts off its pastimes until
the evening; then, when its carnival of two or three hours' duration is
over, retires also to rest, putting out its candle, and so exposing
itself to the dangers which surround other diurnal species during the
hours of darkness. I have spoken of the firefly's pastimes advisedly,
for I have really never been able to detect it doing anything in the
evening beyond flitting aimlessly about, like house flies in a room,
hovering and revolving in company by the hour, apparently for amusement.
Thus, the more closely we look at the facts, the more unsatisfactory
does the explanation seem. That the firefly should have become possessed
of so elaborate a machinery, producing incidentally such splendid
results, merely as a protection against one set of enemies for a portion
only of the period during which they are active, is altogether
incredible.

The current theory, which we owe to Belt, is a prettier one. Certain
insects (also certain Batrachians, reptiles, &c.) are unpalatable to the
rapacious kinds; it is therefore a direct advantage to these unpalatable
species to be distinguishable from all the persecuted, and the more
conspicuous and well-known they are, the less likely are they to be
mistaken by birds, insectivorous mammals, &c., for eatable kinds and
caught or injured. Hence we find that many such species have acquired
for their protection very brilliant or strongly-contrasted
colours--warning colours--which insect-eaters come to know.

The firefly, a soft-bodied, slow-flying insect, is easily caught and
injured, but it is not fit for food, and, therefore, says the theory,
lest it should be injured or killed by mistake, it has a fiery spark to
warn enemies---birds, bats, and rapacious insects--that it is uneatable.