The native snail shell–nesting bee <i>Osmia conjuncta</i> (Hymenoptera: Megachilidae) exploits a local abundance of exotic <i>Cepaea</i> snails (Stylommatophora: Helicidae), choosing empty shells by size, colour, and microhabitat

Abstract For solitary bees, nesting substrate availability may limit population growth. Here, we investigate the of a locally abundant bee Osmia conjuncta Cresson (Hymenoptera: Megachilidae) in empty shells exotic snails, Cepaea spp. Held (Stylommatophora: Helicidae), Hamilton, Ontario, Canada. A literature review determined that O. was sparsely distributed throughout its range, with low relative abundance except for Niagara Region Canada, three sites Maryland, United States America, and focal study area Ontario. The Hamilton field survey five grassland communities found to be most species. average 18.7%, peaking at 87% on one spring day. 1088 snail done site highest abundance. It revealed an 10.87 per square metre cocoons 9.8% shells, averaging 1.6 nest. relation between shell traits cocoon presence indicated preferred intermediate size colour avoided near shrubs. snails increased populations potential consequences local assemblage.