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Solitary Bees With a Twist

Jeffrey Hahn, Asst. Extension Entomologist

Photo 1: Andrenid bee. Jeff Hahn.

Andrenid bees, especially Andrena spp., are common insects that are sometimes seen in yards and gardens in spring. They are small to medium sized insects, about 1/4 - ½ inch long. They are hairy, dark-colored insects, often with a thick mat of yellow hairs on their thorax.

They typically overwinter as pupae and emerge as adults as soon as the weather becomes warm, living for about a month. Andrenid bees nest in the ground, preferring sunny, dry sites with sparse grass or few plants. They create cylindrical tunnels where they spend essentially their entire life preparing these nests for their young. They provision them with pollen balls on which the larvae feed during summer.

Unlike honey bees and bumble bees, which are social insects living in colonies, andrenid bees are solitary insects that live by themselves. They are responsible for all of the work that is required to maintain the nest and provide for the larvae. However, andrenid bees typically live gregariously, i.e. many individual nests in a small area despite the appearance that they are coming from a single nest.

Photo 2: Andrenid bee nests (notice how many there are in this small area). Jeff Hahn.

Fortunately, andrenid bees are gentle and stings are extremely rare. It is possible they might sting if they are mishandled. However, there are many reports of people in close proximity to these bees without being stung.
When dealing with andrenid bees, tolerate them as much as possible. Bees are beneficial because they are pollinators and should be preserved whenever possible. Remember that they are gentle with little risk of stings. They are also only active for about a month and they shouldn't be around much longer this spring. Insecticides are a possibility but should only be used as a last resort.

Photo 3: Cuckoo bee, Nomada sp., entering an andrenid bee nest. Jeff Hahn.

There is a plot twist in one particular andrenid bee site that was observed recently. Another insect was apparently nesting in the ground in same area as the andrenid bees. They were reddish brown with a yellow striped abdomen, few hairs on their bodies, and were a little smaller. After collecting and examining a specimen, they were identified as cuckoo bees, Nomada sp. Cuckoo bees are wasp-like in appearance and are not pollinators like most bees. Instead they are parasitic on other bees, entering and laying their eggs into the host bee's nests so the food gathered will feed the cuckoo bees' young. The world of entomology never ceases to amaze.

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