Queen & Worker:
Head: Black hairs with a dense yellow tuft in the centre of the top of the head (vertex). Face black, longer and thinner than B. sandersoni.
Thorax: Yellow to tawny, except for a small (larger in worker) shiny bare spot at centre, intermixed with black between the wings.
Wings: Lightly and uniformly tinted, veins brownish.
Legs: Black with long black fringe. Front thigh has slight graying. Feet brown.
Abdomen: Segments 1 and 2 are yellow to tawny, and segment 2 might have an indent at centre on lower border. Segments 3 to 6 entirely black. Underside black.
Head: Hair yellow, especially bright below antennae, on top of head in the centre (vertex) and cheeks. Rest of face intermixed with long, black hairs.
Thorax: Bright yellow with a tiny bare spot centrally between wing bases. Black hairs intermixed with yellow on thorax sides.
Wings: Slightly tinted, more so at tips.
Legs: Legs have many long, yellow hairs on thighs. Hairs become darker toward feet. Hind shin (tibia) slender and shiny with some yellow hairs mixed with the black.
Abdomen: Segments 1 and 2 have long yellow hair. Segments 3 to 7 are black. Underside with yellow hairs.
Similar Species: Sanderson’s Bumblebee Bombus sandersoni has very few yellow hairs on top of head and flies later than the Half Black. It is much smaller.
Size: Queen 18.5 mm. Worker 11 to 13.5 mm. Male 12 to 15.5 mm.
Flight Time: May to end of September.
Habitat: Woodlands and forest edges.
Food: Generalist feeder on pollen and nectar from a wide variety of flowers.
Life Cycle: Queen builds nest either above and below ground and sometimes tries to take over the nest of another established queen. She builds a wax honey pot and fills it with honey and pollen, then lays a batch of eggs on the pollen, covering them with a waxed sheet. Eggs are kept warm by the queen. Hatched larvae are continually fed by the queen until they pupate. The first brood become workers and take over nest maintenance and honey & pollen foraging. Queen, workers and males die at the end of the season. Only mated females live to hibernate in sheltered locations until the next spring.
Comments: Essex County – Point Pelee National Park; Ojibway Prairies. Also in Leamington. Kent County – Rondeau Provincial Park.
Parasitized by the Lemon Cuckoo Bumblebee Bombus citrinus.