by Skip Via
skip@westvalleynaturalists.org

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We have several beds of bee balm (bergamot), both native varieties and cultivars, planted around our property to attract bees and hummingbirds, which it does in huge numbers. It’s not uncommon find more than a dozen species of bees foraging for nectar on a single bed.

Lately, I’ve noticed a virtual invasion of a bee species that is new to me–a small, gray striped bee that looks like a cross between a honey bee and a bumblebee. True to form, it’s neither. It turns out that this is an urbane digger bee (Anthrophora urbana).

There are a number of members of the digger bee genus (Anthrophora), and their appearance can be quite different. Like this urbane digger, they are typically small, usually less than half an inch. Their bodies are metallic black (usually) and their abdomens are covered with hair which can range in color from white/gray to orange/brown. The urbane digger bee has distinct white/gray stripes and white/gray hair.

Urbane digger bees, like all digger bees, are strictly solitary bees. But while they live solitary lives in their own holes and do not form colonies as do honey bees, their nests are clustered closely together. This has led some entomologists refer to urbane diggers as “social solitary” bees, as they appear to live in colonies. But they don’t follow a queen and there are no worker urbane diggers. It’s every bee for themselves.

Urbane diggers build their nests in loose soil, either on flat ground or in vertical banks. They are most active June-September, although in more clement weather further south (apparently they are very common in the San Francisco Bay area) they may appear from May-October. The females can sting, but are considered non-aggressive unless attacked. Drones have been described as typically more aggressive in mating than most other bee species, often initiating mating.

Urbane digger bees, like all digger bees, are important pollinators. They will visit a variety of flowers and they are constantly in motion, spreading pollen far and wide. There are no immediate threats to their existence other than loss of habit in developed areas. Because they nest in the ground, some lawn care products (especially those used by commercial big specialists) can kill them or limit their nesting.