The flesh-fly laying its eggs on the carrion-flower is only a striking instance of the mistakes all instincts are liable to, never more markedly than in the inherited tendency to fits of frenzied excitement: the feeling is frequently excited by the wrong object, and explodes at inopportune moments.
_(Remarks about Fireflies and other matters.)_
It was formerly supposed that the light of the firefly (in any family possessing the luminous power) was a safeguard against the attacks of other insects, rapacious and nocturnal in their habits. This was Kirby and Spence's notion, but it might just as well be Pliny's for all the attention it would receive from modern entomologists: just at present any observer who lived in the pre-Darwin days is regarded as one of the ancients. The reasons given for the notion or theory in the celebrated _Introduction to Entomology_ were not conclusive; nevertheless it was not an improbable supposition of the authors'; while the theory which has taken its place in recent zoological writings seems in every way even less satisfactory.
Let us first examine the antiquated theory, as it must now be called. By bringing a raptorial insect and a firefly together, we find that the flashing light of the latter does actually scare away the former, and is therefore, for the moment, a protection as effectual as the camp-fire the traveller lights in a district abounding with beasts of prey. Notwithstanding this fact, and assuming that we have here the whole reason of the existence of the light-emitting power, a study of the firefly's habits compels us to believe that the insect would be just as well off without the power as with it. Probably it experiences some pleasure in emitting flashes of light during its evening pastimes, but this could scarcely be considered an advantage in its struggle for existence, and it certainly does not account for the possession of the faculty.