Adult Danaus plexippus in southern Ontario frequently engage in soaring flight during their late summer migration. They utilize both ascending air currents (lift) produced by winds blowing up slopes and thermals (bubbles or columns of air that are rising because they are warmer and lighter than the surrounding air). The butterflies appear to be very efficient and exhibit different flying techniques when encountering various types of lift. When the weather is favourable, soaring is the main mode of flight and the butterflies achieve heights above the ground of at least 300 m. Extended soaring flight in thermals was always associated with tail winds.A sample of 18 specimens gave an average mass of 566 ± 81 mg and an average wing loading of 0.018 ± 0.002 g/cm2 (1.77 N/m2). Gliding performance parameters were measured for two specimens ballasted to 450 mg and the results were extrapolated to 600-mg individuals. The energetic advantages of utilizing soaring flight in terms of extension of maximum range is discussed.

Worker-male conflict in different bumble bee species is strongly associated with tendency, toward inbreeding. It is hypothesized that the major cost imposed by inbreeding arises from the production of diploid males in place of workers, during the early phases of colony development. The consequent dilution of the labour force slows down colony growth and leads to ultimate reduction in reproductive success. An experiment to test this hypothesis is described, using consanguineously mated queens of B. atratus Fkln. Colonies yielding a 1:1 mixture of males and workers grew significantly more slowly than normal all-worker producing colonies, providing support for the hypothesis.

A re-investigation of the taxonomic status of Bombus sandersoni Fkln. is described. Using multivariate analysis of wing venation data taken from previously identified museum specimens, a non-overlapping separation between sandersoni, B. frigidus F. Sm., and B. vagans F. Sm. was obtained. The Cresson lectotype of B. couperi appears in some respects intermediate between frigidus and sandersoni. Therefore the authors advocate retention of sandersoni as the valid name for the species, while admitting the possibility that this taxon may turn out to be a clinal variant of frigidus.

Statistical analysis of traffic data at the nest entrance of a colony of the yellowjacket, Vespula arenaria (F.), showed no evidence for the operation of social facilitation of the type described by Blackith (1957). As in bumble bees, the appearance of contagion in the temporal distribution of exits and sorties is the result of overall change in flight activity and is not due to social interaction between wasps.