Osmia (Osmia) nigrohirta are black bees with a little to no metallic shimmer on the abdomen. Females have black hair throughout their body with the exception of occasional reddish-brown hairs on the basitarsi and sometimes brown hair on T6 (Peters 1978). Males have yellow to white hair on their head, brownish hair on the thorax, T1–T3 have yellowish-brown hairs, and T4–T7 have black hairs (Peters 1978). Female body length is approximately 13 mm, and male body length is 11–13 mm (Peters 1978).
(modified from Peters 1978)
O. nigrohirta females are easily distinguished from all other Osmia (Osmia) by their almost entirely black pubescence and relatively simple clypeus. Male O. nigrohirta can be very similar in coloration to O. mustelina (Peters 1978). O. nigrohirta males can be differentiated by the more brownish hair on the hind basitarsus and shape of the gonocoxites, which are acutely pointed apically (Peters 1978).
Osmia nigrohirta adults have been recorded in flight during June and July (GBIF 2019e).
Osmia nigrohirta specimens have been collected in Turkey, Lebanon, and Albania (Peters 1978).