What Are Digger Bees and How Do They Impact Your Garden?

When someone mentions bees, most of us picture honeybees, bumblebees or those aggressive carpenter bees that drill into wood surfaces.

There are, in fact, four thousand species of bees native to the United States, and fully one-quarter are ground nesters. Commonly grouped together and referred to as ‘digger bees’ they comprise 70 different species with the greatest number found in western states. Digger bees belong to the family Apidae.

Other bee-like insects also nest in the ground including hornets and yellow jackets. It’s important to correctly identify which type is burrowing into your garden so you can manage them in the best way possible.

Here is everything you need to know about digger bees and why you might want to welcome them in your vegetable and flower gardens.

What Are Digger Bees?

Digger bees are solitary flying insects that dig small round holes in loose, bare, sandy soil in lawns and gardens. Females burrow into the soil to create tunnels and build chambers to lay eggs and raise brood. Underground nests range in size from a few inches to several feet depending on species. Each nest includes separate entry and exit holes.

Females dig a chamber for each egg, line it with wax, and fill it with nectar and pollen to feed the young larvae. A single egg is laid and the chamber is sealed with a waterproof substance. Brood clutches are much smaller than those of colonizing bees with a dozen or fewer egg chambers per nest.

Once an egg is deposited, bees spend up to 11 months underground, developing as larvae and pupating. Only one generation of adult digger bees emerges each spring.

Like all bees, only female digger bees have stingers, however they are reluctant to use them and sting only when harassed or handled. They are shy and retreat into their burrows when approached by humans.

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Identifying Digger Bees

The presence of small holes in dry, bare ground is a sign of digger bees. Holes are about the diameter of a number two pencil and may be surrounded by small mounds of soil often mistaken for ant hills. In areas with large populations, females may dig burrows close to each other, but in most species every female creates and maintains her own underground space.

Bees are 1/4 to 1/2 inch long and variable in color (mostly shiny metallic or dark, but some with markings of white, yellow, or reddish brown).

Females are larger than males with thick hairs on the hindlegs used for collecting pollen. Males have longer antennae and are usually seen flying around a burrow seeking a female to mate.

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

Young digger bees spend most of their life cycle underground, from egg to larvae to pupae, eventually emerging above ground as adults. Males appear first to feed on nectar. Females start building and provisioning their nests almost immediately and, once the burrow is complete, become receptive to male advances.

Once bees mate and females lay eggs, the adult generation dies off and the cycle repeats the following spring.

How Digger Bees Impact Your Garden

Digger bees are important pollinators in flower and vegetable gardens. They are most active in spring when plants are just starting to grow and are of particular importance in the vegetable garden, pollinating early vegetables like squash and beans.

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

How to Prevent Digger Bee Damage In Your Garden

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

Early plant damage is sometimes mistakenly attributed to digger bees when the culprit is more likely a grub, sawfly, or other garden pest. If numbers become a nuisance here are a few organic recommendations for reducing populations. Harsh pesticides are discouraged since they impact other beneficial insects in the garden.

• Water regularly and keep soil moist, especially in late spring and early summer. Female digger bees are drawn to dry soil and won’t burrow in wet ground.
• Mulch around plants to add a soil barrier.
• Use weed barrier fabrics.
• If digger bees affect your lawn, plant new grass in bare spots.
• Remove rocks, bricks, and other solid barriers that bees can dig under to shelter their burrows.
• Pour hot, soapy water down existing nest holes to drown larvae.