Mutual Aid by Peter Kropotkin

M. C. Piepers has published in Natuurkunding Tijdschrift voor Neederlandsch Indië, 1891, Deel L. p. 198 (analyzed in Naturwissenschaftliche Rundschau, 1891, vol. vi, p. 573), interesting researches into the mass-flights of butterflies which occur in Dutch East India, seemingly under the influence of great draughts occasioned by the west monsoon. Such mass-flights usually take place in the first months after the beginning of the monsoon, and it is usually individuals of both sexes of Catopsilia (Callidryas) crocale, Cr., which join in it, but occasionally the swarms consist of individuals belonging to three different species of the genus Euphoea. Copulation seems also to be the purpose of such flights. That these flights are not the result of concerted action but rather a consequence of imitation, or of a desire of following all others, is, of course, quite possible.

Bates saw, on the Amazon, the yellow and the orange Callidryas "assembling in densely packed masses, sometimes two or three yards in circumference, their wings all held in an upright position, so that the beach looked as though variegated with beds of crocuses. " Their migrating columns, crossing the river from north to south, "were uninterrupted, from an early hour in the morning till sunset" (Naturalist on the Amazon, p. 131).