Art. XXXVII.—On the Unusual Abundance of Certain Species of Plume-moths during the Summer of 1894–95.
[Read before the Wellington Philosophical Society, 21st August, 1895.]
The laws governing the relative abundance of different species of animals and plants are so obscure, and at present so little understood, that it is always desirable to record the appearance of any species when it occurs in unusual numbers.
Last summer I noticed that the three species of forest-dwelling plume-moths (Pterophorus monospilalis, P. lycosema, and P. furcatalis) were phenomenally common here. Pterophorus monospilalis, a pure-white species, one of the most delicately beautiful insects we have in New Zealand, was to be found in the utmost profusion, as many as three or four specimens being disturbed from amongst the ferns and dense undergrowth at once. Pterophorus lycosema, distinguished by having a broad band of brown on the fore-wing reaching as far as the end of the posterior digit, was also extremely abundant, though not quite so common as P. monospilalis. P. furcatalis, distinguished by having a broad band and both digits of the fore-wings brown, was commoner than usual, but much scarcer than either of the two preceding species.
I have much pleasure in exhibiting series of all three species before the Society this evening, and have mounted them on a dark background in order that their extremely elegant appearance may be seen to advantage. I ought perhaps to explain that, as a rule, these three insects are not very common—that is to say, one would not expect to meet with more than one or two specimens during a day's collecting in a favourable locality.