In a field experiment, the bumblebee, B. ternarius, visited milkweed patches harboring crab spiders, Misumena vatia, at a lower frequency than patches free of crab spiders, and honeybees showed a similar but non-significant trend. Two other bumblebee species, B. terricola and B. vagans, did not avoid the spider patches. The latter two species are larger than B. ternarius and honeybees and suffer lower crab-spider predation. As far as we know, this is the first field study documenting negative effects of predators on flower visitation rate by pollinator populations. Our study suggests that pollinator response to predation may influence pollinator-plant interactions.