Temporal, chemical and spatial separation of nitidulid beetles (Coleoptera) were examined with baited traps over two seasons (1989 and 1990) in temperate North America. In both years, Stelidota geminata (Say), Carpophilus lugubris Murray, Glischrochilus fasciatus (Olivier) and Glischrochilus quadrisignatus (Say) comprised 95-99% of all nitidulid beetles collected. These species were collected in greatest numbers in July, except for C. lugubris, which was collected in high numbers in July and late September in 1990. Peaks in trap catch were preceded, in most cases, by high percentages of gravid females. Carpophilus hemipterus (L.) was the only nitidulid species that showed a significant preference for Candida krusei-inoculated fruit and vegetable baits over aseptic baits in 1989. For three of the four dominant species, the response to baits was broad : C. lugubris was the only species that exhibited a specialized response to one substrate over the entire trapping period in both years. G. quadrisignatus showed a seasonal or local specialization to maize baits in the spring of 1989 and at two of the three locations in the spring of 1990. There was a clear division in habitat preference for the dominant species : C. lugubris and G. quadrisignatus occurred almost exclusively in agricultural settings, whereas G. fasciatus occurred predominantly in woodlots. Numbers of S. geminata fluctuated seasonally, showing a preference for woodlots early and late in the season and a preference for agricultural settings throughout most of the summer. Less common nitidulid species also displayed habitat preferences. Although the Nitidulidae have had a longer association with climax communities than with ruderal communities, the diversity of nitidulid beetles was similar in the two habitat types. This may be because many of the resources these beetles use for food and oviposition sites in climax communities are ephemeral and closely related to the resources that they use in ruderal communities (i.e. wild versus domesticated strawberries, wild versus domesticated cherries and hawthorn fruit versus apple).