Red mason bees are solitary bees which are commonly found in gardens and urban areas. Many people will have seen the bee hotels which you can buy now from many garden centres and similar locations which are perfectly designed to create a nest site for this species.
There are several species of mason bee in the UK but the red mason – Osmia rufa – is the most common. They are prolific pollinators – estimated to be 120-200x more efficient than the honey bee which makes them a real benefit to any garden, especially those with fruit trees whose flowering period coincides well with the time that these bees are on the wing.
Red mason bees naturally nest in hollow plant stems or holes in cliffs. They also make use of the crumbling mortar of old buildings but their needs can be easily accommodated in the hollow tubes which are the common constituents of bee hotels. After mating, the female bees lay their eggs in the nesting tubes. Each egg is laid and provisioned with pollen and nectar for the young to eat when it hatches. After each egg is laid, a mud-wall is created between it and the next cell which she lays to that the tube, when complete, is a series of individual nest cells. Think a packet of rolo’s where the wrapper is the tube, the chocolate is the mud partition and the caramel inside is the egg, nectar and pollen!
In order to build these cells, the mason bees need to gather mud from a source close to the nest. I found such a ‘mud mine’ down by the banks of the River Witham in Grantham. Close to the waters edge, where the mud is damp, there were small holes which were visited by several bees at the same time, all intent on extracting mud. They scrape this from the surface, roll it into a ball and carry it back to their nest in their mandibles. They seem very faithful to a good location – some of the bees were scraping the mud from the banks on their own, but many used the same spot which had clearly been excavated by several bees over many trips.
Red mason bees are on the wing from around March until June so keep an eye out for them in your back garden and, if you can, provide them with their own nesting site in the form of a bee hotel. If there is no mud source nearby, you can help them out with a tray of damp soil which they will use to line their cells. Your payment will be the services of a highly efficient garden pollinator!