Leafcutter Bees

By Adriane Good, MSU Extension Pondera County

Recently I received a call about a strange mass underneath the siding of a house near Valier. The mass was full of small greenish-brown tubes. Upon closer inspection, it turned out that the mass was a leafcutter bee nest!

Leafcutter bees are great pollinators and helpful to have around your yard. They are essential pollinators for some native plants, and they have been semi-domesticated in some areas to help alfalfa seed production. Next time you venture across the border into Southern Alberta, you might see some small tents in alfalfa fields - those belong to leafcutter bees!

Leafcutter bees are quite small – ranging from 1/5 of an inch to an inch long. They resemble small honeybees with their black and yellow coloring. They do their important job as a pollinator by catching and carrying pollen on the underside of their abdomen. Leafcutter bees like most broadleaf plants, but they have a particular fondness for lilacs, roses, and ash trees.

Leafcutter bees are solitary animals, unlike other insects such as honeybees and ants. Instead of living in colonies and building a nest together, leafcutter bees build nests by themselves and the females do all the work rearing their young. The nests of leafcutter bees contain several small cells that form a tube 4-8 inches long. They make these cells out of leaf cuttings, nectar, and pollen. Once the adult leafcutter bee lays her eggs in the nest, the young bees will stay inside and develop to adulthood, ready to emerge in the next season.

Leafcutter bee nests found under the siding of a house.

You may not notice the bees themselves in your yard, but you may see some evidence of leafcutter bee damage in your plants. To acquire the leaf cuttings for their nests, the leafcutter bees cut out small semi-circles from the leaves of plants. This damage is purely aesthetic and won’t hurt the plant at all. Leafcutter bees are also very non-aggressive, so as long as you aren’t bothering them, they won’t sting you. If they do, no worries, they have a very mild sting. The bees tend to build their nests in soft, rotting wood or other places they have easy access to. Unlike other insects that build their nests in wood, leafcutter bees don’t burrow further into the wood. So, the nest that was found under the siding of a house wasn’t causing any damage!

Evidence of leafcutter bee damage on a lilac.

Leafcutter bees are one of the best insects to have in your yard. If you find a nest in a place where you would not like a nest, remove it and then seal up any cracks you can find, and they probably won’t go back there. If you find some damage on your plants and you want to protect them, you can cover them with cheesecloth or loose netting to prevent the bees from getting to them. If you don’t mind a few holes in your plant’s leaves though, I highly encourage you to let the leafcutter bees roam your yard to continue their important pollination work!