Plants affected
Many plants, but roses are a particular favourite.
Symptoms
The female bee uses her jaws to cut neat, elliptical segments out of the leaf margins, particularly of roses. The adult bees are more hairy and broader than a honeybee. Leaf-cutting bee females are 10-15mm long and the underside of the abdomen is covered in ginger hairs. The nests are made in tunnels in rotten wood, hollow plant stems or in flower pots and seed trays, especially where the compost has dried out.
Cause
This is the work of leaf-cutting bees that use the leaf segments
in the construction of their nests. Rose leaves are particularly
favoured, but other plants are also used. The female bee carries
one leaf piece at a time back to her nest.
Each thimble-shaped leaf cell is then stocked with a mixture of nectar and pollen on which the bee lays an egg, before capping the cell with circular pieces of leaf. The process is repeated until the nest may contain up to 20 cells. The nests are sometimes found when glasshouse plants are being repotted or old seed trays emptied; by then the leaves may have become greyish brown and the cells may contain white grubs which will pupate and emerge as adult bees the following year.
These bees are solitary with each female having her own individual nest that she constructs and provisions on her own. The females have stings but lack aggression and do not chase or sting people. Most plants can tolerate the damage, although small plants may suffer a significant loss of leaf area. Nests in flower pots have little impact on the plant unless it is growing in a small pot.
Control
Leave them be. Like all bees, leaf-cutters are beneficial in the garden as they act as pollinators of flowers, so they should not be persecuted unnecessarily. If small plants are suffering significant leaf loss, swat the bee when it comes to collect another piece of leaf. It is quite possible that all the damage on a plant is due to a single bee, as it will repeatedly visit a plant that has suitable leaves.