Swarming activity patterns and seasonal decline in adult size in some caddis flies (Trichoptera: Leptoceridae)

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Abstract
Six species of swarming caddis flies were studied at two lakes in southern Sweden. Some species showed a differentiated swarming phenology as well as diurnal activity patterns, although swarming was usually most pronounced at dusk. Swarming activity of the species also showed small differences in sensitivity to wind velocity, temperature and illumination intensity. In Mystacides azurea there was a tendency for unmated females to approach the male swarms earlier in the evening swarming periods than did the mated ones, probably because mated females alternate their activity between egglaying and mating. The number of observed pair formations was correlated with the number of swarming males, indicating that males had their activity peak when the number of receptive females was highest. Emerging adults of M. azurea and males of Athripsodes aterrimus showed a significant seasonal decline in body size (wing length).