Two deer fly species, Chrysops mitis Osten Sacken and Chrysops excitans Walker, were collected by sweep-netting around human bait on five collection dates in Algonquin Provincial Park, Ontario. Distribution patterns of the two species at two sites (abandoned airfield and Davies bog), in two habitats (open and forest edge), and at two times of day (morning and afternoon) are analysed. Chrysops excitans was more frequently collected than C. mitis. Regardless of site, both species are more common in the morning than the afternoon collections and both are more common in the open than the forest-edge habitats. Chrysops excitans was the larger species (based on wing length measurements) and its size was constant regardless of site, habitat, and time of day. In contrast, afternoon-collected C. mitis were larger than morning-collected flies at the Davies bog site. The crop contents of 241 flies were identified using thin-layer chromatography. Using melezitose and stachyose as honeydew-indicator sugars, the relative importance of homopteran honeydew and floral nectar as carbohydrate sources for these flies was determined. We found no significant differences among species, sites, habitats, or times of day. Overall, 52.8% of C. excitans and 51.1% of C. mitis had recently fed on homopteran-derived honeydew sugars, underscoring the importance of this carbohydrate source for the haematophagous Diptera.