A study was conducted at two peatland sites in southern Ontario to test the hypothesis that flowering-time diversification among ericaceous plants has resulted from interspecific competition for pollinators. Exclusion of pollinators from plants indicated that insect visitation was important to the seed set of all species tested. The species composition of insects visiting five ericaceous species overlapped considerably, which suggested that interspecific competition could be responsible for observed differences in peak flowering times. While previous experimentation has demonstrated that seed set is influenced by intraspecific competition for pollinators, evidence of interspecific competition is lacking. The inconstancy of pollinators rather than their low numbers is proposed as an additional explanation of why the peak flowering times of ericaceous shrubs do not overlap.