mason bee colony made from illy coffee tin, my allotment, London, England

‘mason bee’ is the common name for a species of bees in the genus Osmia, of the family Megachilidae, they are named from their habit of making compartments of mud in their nests, which are made in hollow reeds/canes or holes in wood made by wood-boring insects

 unlike honey bees or bumblebees, mason bees are solitary; every female is fertile and makes her own nest, and there are no worker bees for these species, they produce neither honey nor beeswax

the bees emerge from their cocoons in the spring, with males the first to come out, they remain near the nests waiting for the females, when the females emerge, they mate - the males die, and the females begin provisioning their nests.

 mason bee females like to nest in narrow holes or tubes, typically naturally occurring tubular cavities, most commonly this means hollow twigs, but sometimes abandoned nests of wood-boring beetles, they do not excavate their own nests

the material used for the cell can be clay or chewed plant tissue

because mason bees provide an invaluable pollination service for gardeners it is possible to buy ‘nests’ for females to use – or you can make your own, as i have, out of an old coffee can and some hollowed out bits of bamboo

females then visit flowers to gather pollen and nectar, and many trips are needed to complete a pollen/nectar provision mass - once a provision mass is complete, the bee backs into the hole and lays an egg on top of the mass, she then creates a partition of mud, which doubles as the back of the next cell. the process continues until she has filled the cavity, female-destined eggs are laid in the back of the nest, and male eggs towards the front.

 once a bee has finished with a nest, she plugs the entrance to the tube, and then may seek out another nest location

 by the summer, the larva has consumed all of its provisions and begins spinning a cocoon around itself and enters the pupal stage, and the adult matures usually in the  winter, hibernating inside its insulatory cocoon until warm spring weather arrives

mason bees are increasingly cultivated to improve pollination for early spring fruit flowers, they are both beneficial and benign, since they both pollinate plants and do not sting

 one of my coffee tin mason bee colonies showing both occupied sealed tubes and empty tubes