170 The Naturalist in La Plata.
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
Nature's Night Lights. 171
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.
The theory of warning colours is an excellent one, but it has been pushed too far. We have seen that one of the most common fireflies is diurnal in habits, or, at any rate, that it performs all the important business of its life by day, when it has neither bright colour nor light to warn its bird enemies; and out of every hundred species of insect-eating birds at least ninety-nine are diurnal. Raptorial insects, as I have said, feed freely on fireflies, so that the supposed warning is not for them, and it would be hard to believe that the magnificent