Twenty-nine Sorex hoyi and one hundred and forty-one Sorex cinereus were pitfall trapped in seven bogs in northern Lower Michigan. Habitat consisted primarily of a Sphagnum spp. mat with sedges (Carex spp.), Chamaedaphne spp., Kalmia spp., Ledum spp., and other bog shrubs dominating the understory. The overstory consisted of widely dispersed stands of spruce (Picea) and tamarack (Larix) or alder (Alnus). Weather data showed no correlation with abundance of either species of shrew, but temperature fluctuations were reduced by 50% within the Sphagnum mat and may provide an insulating layer for shrews. The abundance of S. hoyi was correlated with arthropod abundance. Stomach analyses indicated that S. hoyi and S. cinereus have similar diets. Formicids accounted for approximately 50% of the identifiable gut material for both species. Formicids and other prey in the 2-5 mm size class were also the most abundant prey items taken inpitfall traps at the seven localities trapped. No first-year S. hoyi (aged based on tooth wear patterns) were sexually mature, whereas 90% of the second year animals were sexually active when captured, indicating that S. hoyi do not breed in their first year of life. Approximately 4% of first-year S. cinereus were reproductively mature, suggesting that they may breed in their first year. The proportion of adults (individuals in their second year) of both species decreased throughout the summer, while juveniles increased markedly toward the end of the summer.