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Latitudinal body‐size gradients for the bees of the eastern United States

Do insect body sizes vary latitudinally? Cushman et al. (1993) recently conducted a comparative analysis of formicine and myrmicine ant species in northern Europe and found that worker body sizes decreased with decreasing latitude in both subfamilies. In contrast, Barlow (1994) analysed butterflies in the Afrotropics and Australasia and found that body sizes (wing spans) generally increased towards the tropics. In a second study of butterflies, Hawkins & Lawton (1995) analysed four butterfly families and the skippers in the Nearctic, Afrotropics, Europe and Australia, and found that most families did not vary latitudinally in forewing length, and in the few cases where they did, trends were inconsistent in different biogeographical realms. Therefore there is some question about the direction and generality of latitudinally derived trends in insect body sues. Ants and butterflies differ in a number of obvious ways, including their taxonomy (and hence their evolutionary histories), biology, behaviour, and trophic relationships. For these reasons it is uncertain what the different results for the two groups signify. Before either result can be considered more relevant to the vast majority of insect taxa, it is necessary to extend such analyses into other taxonomic groups. In this note I test for latitudinal gradients in body size for the bees of the eastern United States, a group more taxonomically allied to ants than are butterflies. The data were extracted from Mitchell (1960, 1962), which gives body size ranges and the states where recorded for all known native bee species. The geographic area covered represents all of the states east of the Mississippi River, comprising twenty-six states and the District of Colombia. Body size was measured as the midpoint of the range of body lengths of females (for asocial species) or workers (for social species). Species for which only the body lengths of males were given were excluded from the analysis. The