Osmia bicornis, or Red Mason Bees, are a solitary bee specialising in aerial nest building. You can find these bees in the holes in walls and timber, or sometimes they'll choose the hollowed-out stems of plants. Having found a suitable site for a nest, a female will then start to forage for nesting materials, more specifically, mud. They use this to mould individual chambers, in which they lay one egg on a ball of sticky pollen. If you look closely, you can sometimes see females carrying pellets of mud back to nesting sites. These bees are particularly fond of flowering fruit trees. O. bicornis is described as a docile bee, who are reluctant to sting.