These are leafcutter bees, which cut pieces of leaf and carry them off to build their nests. I have found the following information about them from the Bumblebee.org website : Leafcutter bees cut holes and semi-circles out of rose leaves, and other leaves, to line the cells in their nest. Leafcutter bees nest in a variety of places, in the ground, under stones, in cavities in wood and stone, pithy plant stems, and in dead wood.
Leafcutters do not have pollen baskets on their legs as bumblebees and honeybees do, but carry the pollen in hairs on the underside of the body.
The female bee places a supply of honey and pollen in the cell; lays an egg on this, then seals the cell and builds the next one in the cylindrical hollow. The cells look like stubby cigars - see right.
Once she has sealed the last cell she goes off and dies. When the new adult bees are ready to emerge they eat their way through the leaf parts. The last egg laid is the first to hatch. The last eggs laid are usually males, and they hang around on nearby flowers waiting for the females to emerge.
In the UK they fly from June to August. The female uses rose, birch, ash and many other leaves as long as they have a serrated edge. The tunnel diameter is 7 -8 mm, and 9 - 12 pieces of leaf are needed for each cell. The cells are thimble shaped inside, and each is sealed with 4 - 12 circular pieces of leaf.
There are usually 6 - 10 cells per nest. Each cell takes the bee around 6 - 8 hours of work to construct, provision with honey and pollen and to lay an egg. She does not have pollen baskets but carries pollen back to the nest in the bright orange brushes on the underside of her abdomen.
At night she rests in the nest entrance facing outwards and will bite anything that tries to enter. The eggs hatch in 12 - 16 days, feed then spin their cocoon 17 -18 days later. Fecal pellets help stick the outer layer of the cocoon to the inner leaf layer of the cell.
