What are Digging Wasps and How Do They Affect Your Garden?

When someone mentions bees, most of us picture honeybees, wasps, or those aggressive carpenter bees that drill holes into wooden surfaces.

There are actually four thousand native bee species in the United States, and a quarter of them are ground nesting. Often grouped together and referred to as ‘digger bees’, they include 70 different species with the largest numbers found in the western states. Digger bees belong to the family Apidae.

Other bee-like insects that nest underground include wasps and yellow jackets. It is important to identify exactly which species are burrowing in your garden so that you can manage them in the best possible way.

Here’s everything you need to know about digger bees and why you should welcome them into your vegetable and flower gardens.

What is a borer?

Mining wasps are solitary flying insects that dig small, round holes in loose, sandy soil in lawns and gardens. Females burrow into the soil to create tunnels and construct chambers to lay eggs and raise larvae. Underground nests range in size from a few inches to several feet, depending on the species. Each nest has a separate entrance hole.

The female excavates a cavity for each egg, lining it with wax and filling it with nectar and pollen to feed the young larvae. One egg is laid and the cavity is sealed with a waterproof sealant. The larval nests are much smaller than those of resident bees, with a dozen or fewer egg chambers per nest.

After laying eggs, the wasps remain underground for up to 11 months, developing into larvae and pupae. Only one generation of adult burrowing wasps emerges each spring.

Like all bees, only female digger bees have a stinger, however they are reluctant to use it and only sting when disturbed or touched. They are shy and retreat into their burrows when approached by humans.

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Identification of digger wasps

The presence of small holes in dry, bare ground is a sign of a subterranean wasp. The holes are about the diameter of a number two pencil and may be surrounded by small mounds of earth that are often mistaken for ant hills. In areas with large populations, females may burrow close together, but in most species, each female creates and maintains her own underground space.

Bees are 1/4 to 1/2 inch long and come in a variety of colors (mostly shiny or dark metallic, but some are white, yellow, or reddish brown).

Females are larger than males with thick hairs on their hind legs used to collect pollen. Males have longer antennae and are often seen flying around the burrow looking for females to mate with.

Males also collect nectar from flowers but do not collect pollen or assist the female in nest building or raising young.

Young subterranean bees spend most of their life cycle underground, from egg to larva to pupa, eventually emerging to the surface as adults. Males emerge first to forage for nectar. Females begin building and provisioning their nests almost immediately and, once the nest is complete, become receptive to male advances.

After the bees mate and the female bees lay eggs, the adult generation dies and the cycle repeats the following spring.

The Impact of Digging Bees on Your Garden

Underground bees are important pollinators in flower and vegetable gardens. They are most active in spring when plants are just starting to grow and are especially important in vegetable gardens, pollinating early vegetables such as squash and beans.

Many species also prey on insect pests. From roots to flowers to fruit, they do not damage any part of the plant and improve root and soil health by aerating the soil.

How to Prevent Damage Caused by Digging Bees to Your Garden

Mining bees are beneficial insects that do more good than harm and are an important part of our ecosystem. Some species are declining due to habitat loss so let’s try to live with them.

Initial plant damage is sometimes mistaken for wasps when the culprits are more likely to be grubs, sawflies, or other garden pests. If the numbers become a nuisance, here are some organic tips to reduce the numbers. Avoid using harsh pesticides as they can affect other beneficial insects in the garden.

• Water regularly and keep the soil moist, especially in late spring and early summer. Female digger bees are attracted to dry soil and will not burrow in wet soil.
• Spread mulch around the plant to create a soil barrier.
• Use weed control fabric.
• If bees are affecting your lawn, plant new grass in the bare spots.
• Remove rocks, bricks, and other solid obstructions that bees can dig under to make shelter for their burrows.
• Pour hot soapy water down existing nesting holes to drown the larvae.