while the larva is of protective colours, and therefore almost certainly edible. A much more abundant moth, of about the same size and appearing about the same time, is Spilosoma menthrasti, also white, but in this case both it and its larva have been proved to be inedible. The white colour of the female Diaphora, although it must be very conspicuous at night, may, therefore, have been acquired in order to resemble the uneatable Spilosoma, and thus gain some protection.[1]
Mimicry among Protected (Uneatable) Genera.
Before giving some account of the numerous other cases of warning colours and of mimicry that occur in the animal kingdom, it will be well to notice a curious phenomenon which long puzzled entomologists, but which has at length received a satisfactory explanation.
We have hitherto considered, that mimicry could only occur when a comparatively scarce and much persecuted species obtained protection by its close external resemblance to a much more abundant uneatable species inhabiting its own district; and this rule undoubtedly prevails among the great majority of mimicking species all over the world. But Mr. Bates also found a number of pairs of species of different genera of Heliconidæ, which resembled each other quite as closely as did the other mimicking species he has described; and since all these insects appear to be equally protected by their inedibility, and to be equally free from persecution, it was not easy to see why this curious resemblance existed, or how it had been brought about. That it is not due to close affinity is shown by the fact that the resemblance occurs most frequently between the two distinct sub-families into which (as Mr. Bates first pointed out) the Heliconidæ are naturally divided on account of very important structural differences. One of these sub-families (the true Heliconinæ) consists of two genera only, Heliconius and Eueides, the other (the Danaoid Heliconinæ) of no less than sixteen genera; and, in the instances of mimicry we are now discussing, one of the pairs or
- ↑ Professor Meldola informs me that he has recorded another case of mimicry among British moths, in which Acidalia subsericata imitates Asthena candidata. See Ent. Mo. Mag., vol. iv. p. 163.
