Butterfly Swarms

Abstract

WITH reference to the case mentioned in NATURE, vol. xx. p. 220, I agree with your correspondent that “local fecundity” cannot be the cause of the great number of Vanessa cardui observed this year in the south of England, more especially as this species does not emerge from the chrysalis until the end of July at the earliest. It therefore appears to me probable that the specimens observed have migrated (having hybernated) from the Northern Counties or even from Scotland, in consequence of the exceptional severity of the weather this season. I would also suggest that the “periodical abundance” of this butterfly, as also that of Colias hyale and Edusa, besides several others, may be caused by some peculiarity in the food-plant itself. This is rendered more likely by the fact that both Colias hyale and Edusa, which feed upon plants of the Leguminous order, and often of the same species, appear in great abundance at the same period.