Leafcutter bees important insects of western US

Submitted Photo The damage leafcutter bees may cause to your plants is necessary for the creation of their homes.

If you happen to notice semi-circular or circular notches in your plant leaves, that would be the work of leafcutter bees. These small bees are important native insects of the western United States. They are often essential pollinators of native wild plants, as they are 15 times better pollinators than honeybees. Some leafcutter bees are even semi-domesticated to help produce alfalfa seed.

These small, busy bees are a half inch long with gray to black stout bodies. They are very hairy with abdomens showing white stripes. Leafcutter bees are not aggressive and sting only when handled. Their sting is much less painful than that of a honeybee or yellowjacket wasp. Though these bees are may be deemed friendly, their habits of leaf cutting and nesting in soft wood or plant stems often attracts attention and concern.

The damage leafcutter bees may cause to your plants is necessary for the creation of their homes. The nests are built in soft, rotted wood, in thick stemmed, pithy plants such as rose stems, or in material that is easy for the bee to cut though and excavate. Nest tunnels may extend several inches deep and coarse sawdust may be deposited at the entrance. This sometimes causes confusion for us, thinking that other wood nesting insects are at work, such as carpenter ants. Leafcutter bees will only tunnel though soft, rotted wood and do not cause damage to homes or other wooden structures.

Once the tunnel and nest are built, it needs a bee woman’s touch. These little bees start collecting fragments of leaves. Semi-circles, three-quarter inch in diameter, are chewed or cut from the edges of leaves. They may cut from many types of leaves; however, they do prefer certain kinds – rose, green ash, lilac, and hosta are just a few. Normally, the removal of the leaf tissue does not cause too much damage to the plant. The pieces of leaves that are removed are not eaten, but rather carried back to the nest and used to construct nest cells in the previously built tunnels. Each cell is supplied with nectar and pollen and the female then lays an egg and seals the cell.

Adult females lay roughly 35 to 40 eggs during their short lives of up to two months. Females make up only 33% of their population, therefore three larvae are needed to replace one female bee. Individual female leafcutter bees do all the work of rearing; including digging out nesting areas, creating nest cells, and providing their young with food. The male leafcutter bees only have one main purpose – to fertilize the female. Once his job is complete, he dies.

Leafcutter bees are solitary bees, meaning that they do not produce colonies as other social insects, such as honeybees, yellowjackets, ants, etc., do. No nests are shared, but leafcutter bees do like company and often build their nests near each other. Leafcutter bees have a short flying range of only 300 feet from their bee house and you can be sure they are busy at work nearby in your garden or field. Leafcutter bees are active in the warm summer months and they are perfect for pollinating squash, melons, cucumbers, peas and other summer vegetables and fruits.

The number of these high-value pollinators continues to decline; using pesticides to rid them from your yard is unnecessary. I advise, to those of us being visited by leafcutter bees, to please simply leave them alone and they will leave you alone. These poor, little leafcutter bees already have a large number of parasitic enemies to deal with, the last thing they need to worry about is someone spraying pesticides on them.

Happy Gardening!


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