Mountain Mason Bee

A small matt black bee, the females are 10mm long and show some pale hairs on the body while the males are slightly smaller and have an entirely black pubescence over their body.

In Scotland Osmia inermis was found mainly on exposed, base-rich uplands, between 260–430 m above sea level. Favoured habitat there comprises exposed sheep pasture on low, dry hillocks on a south-facing mica-schist escarpment with a vegetation of heavily-grazed heather, with lichen and moss predominating amongst it. Near to the site the likely forage plants used by the bee there included Lotus corniculatus, Ajuga reptans and Vaccinium myrtillus Otherwise the species has an Arctic-alpine distribution, being found at low altitudes north of the Arctic Circle and in more montane locations further south. The chrysidid wasp Chrysura hirsuta is known to have been reared from Scottish nests of Osmia inermis. After hatching the larva of the parasitoid attacks the bee larva when it has spun its tough cocoon. When mature the C. hirsuta larva spins its own cocoon inside the bee larva's cocoon. C. hirsuta seems to have an obligate, minimum, two-year life cycle which parallels that of O. inermis.