Insect Swarms

Abstract

THIS year being remarkable for “insect swarms,” it is important that all possible information about them should be gained, so as to satisfactorily account for these phenomena. As to Vanessa cardui, which has been abundant throughout the spring and summer, it is possible that some of those specimens which occurred in the spring were the result of a migration from the Continent, but there is no doubt that the specimens which are now seen are nearly, if not all, bred in this country from ova deposited by the spring specimens, quite sufficient time having elapsed for the metamorphosis. With regard to Plusia gamma, I am of opinion that all the specimens seen, and they have been in profusion here from about August 10 till the present time, have been bred in this country. My reason for so believing is that the larvæ were most abundant in the spring, doing damage in gardens to a great extent. Some of these larvæ I fed up, the perfect insects emerging at the time P. gamma first appeared in abundance. My experience of the swarms of P. gamma is that they moved in no particular direction, merely passing in numbers from flower to flower, flowers being scarce this year, any apparent migration being simply a search for more flowers. Instead of putting the cause of these swarms down to “migration,” endeavours should be made to discover the causes of the extraordinary periodical fecundity. It is quite probable, too, that next year, P. gamma and V. cardui will be scarce, as is frequently the case with Colias edusa and hyale after a year of abundance.