Intraspecific variation in diet and/or foraging behaviour is one way in which species are able to occupy wide geographical areas with variable environments. <i>Myotis lucifugus</i> (Le Conte, 1831), a primarily aerial insectivorous bat, consumes spiders in low temperatures at the start and end of summer in Northwest Territories, but in Alaska, it consumes spiders all summer, even during high aerial-insect abundance. There are no competitors of <i>M. lucifugus</i> in Alaska, but there are in Northwest Territories, suggesting that aerial insect abundance and competition from gleaning bats influences when <i>M. lucifugus</i> consumes spiders. In the Kananaskis area of the Rocky Mountains of Alberta, we investigated spider consumption by <i>M. lucifugus</i>, and <i>Myotis evotis</i> (H. Allen, 1864), a species more adept at gleaning, to better understand when bats consume spiders. Fecal sample analysis indicated that <i>Myotis evotis</i> consumed spiders all season long, with greater consumption when the bats were caught near water. <i>Myotis lucifugus</i> did not consume spiders at all. This suggests that <i>M. lucifugus</i> opportunistically consumes spiders when encountered, but does not encounter them in Kananaskis where it forages primarily over open water, unlike in Northwest Territories where it forages in the interior of forests and may encounter spiders more frequently.