There’s a lot that goes into planting and maintaining a garden, and it can be quite troubling to find leaves with half moon shapes eaten out of them.

There are a few insects that munch on leaves, such as caterpillars and grasshoppers, but the Big Horn Basin is also home to many leaf cutter bees. Unlike hungry pests, these little bees are not eating the leaves for food. They use the material to create nests for their young. And they’re actually very important to a niche agricultural industry in the Basin. For this reason, gardeners looking to control pests should take extra care when dealing with these insects.

When people think of bees, they most often think of a hive full of the insects, all working together to produce sweet honey. 

Leaf cutter bees, however, are loner types. The introverted females emerge in late spring and go find a mate. After that, they’re done socializing for the rest of their lives. 

The females make their nests in rotten wood or a small, existing hole, lining the hole with the pieces of leafy material they collect. They throw in some pollen and nectar for their little one to feed on, and lay a single egg. The cell is then sealed. Nests can contain a dozen cells or more, but they have only one mother. The baby bees spend the whole winter inside the cell, feeding on the provisions left by the mama bee, until they emerge in spring. 

Here in the Basin, some farmers develop alfalfa for seed rather than forage, and leaf cutter bees are key to making it a productive industry. Farmers keep the larvae in refrigerated boxes and turn up the heat come spring. They then move the boxes to huts sometimes seen out in the alfalfa fields.

The crucial role of leaf cutter bees in pollinating alfalfa seed crops can be traced to a kind of spring that’s located down inside the plant’s flower. When a larger honey bee reaches down to sip out the nectar, the spring trips and punches the bee right in its fuzzy face. Honey bees can learn to avoid getting punched in the face by an aggressive alfalfa flower, but the method prevents pollination. 

Leaf cutter bees, however, are small enough to avoid getting whacked by the springy alfalfa flower, so they make the perfect pollinators for the crop.

Like all bees, leaf cutter bees fly around for miles, and in the course of collecting leaf material, pollen, and nectar, they can pick up diseases, parasites and pesticides. If those poisons and ailments spread between bees, entire populations can die. That can have a detrimental effect on farmers.

Many Basin farmers import bees, mainly from Canada. The Wyoming Department of Agriculture inspects all imported bees as a means to protect their health. 

“Thanks to this program, Wyoming has some of the healthiest bee populations in the U.S.,” said Cort Jones, with the Wyoming Department of Agriculture’s Division of Technical Services.

Jones takes samples of all shipments of bees, lays the samples out on trays, and X-rays them. He then determines if the shipment contains any parasites or diseases. In some cases, imported bees that carry diseases and parasites have to be turned away. 

“They’re basically regulated like livestock,” Jones said. 

When it comes to insecticides, leaf cutter bees can pick them up and carry the poisons back to their nests. For that reason, gardeners should be very careful using chemicals to control leaf cutter bees. Not only are the bees vital to a key agricultural product in the basin, the insects are largely beneficial as pollinators.

Over the past decade, following widespread hive collapses of all types of pollinator populations, the federal government got involved with better management of the insects. 

The Environmental Protection Agency has a number of tips for household pesticide use. It’s good to follow all requirements on the pesticide labels, use them only when necessary, keep them out of waterways and only apply them to specific areas needing treatment. Bees forage during the day, so gardeners can minimize impacts by applying insecticides at night. 

There is also the option to just ignore the problem. Leaf cutter bees’ cuts are so precise that they rarely hurt the plant’s overall health, and especially with vegetation like fruit trees, the bees are an indispensable pollinator. 

“They’re very beneficial,” Jones. 

While the cuts on the leaves may not look very nice, the bees’ benefits far outweigh their impact on garden aesthetics.