Andrena

Photo by Hartmut Wisch
Andrena – digger bees/miner bees (family Andrenidae)
by Lisa Schonberg and Mace Vaughan (Xerces Society) and Gretchen LeBuhn (SFSU)

Genus summary: Andrena is a large, well known genus that occurs in the Americas, Eurasia and the Old World Tropics with over 1300 species. It. There are over 1300 species worldwide, 454 in the Americas (Michener 2000), and 112 in New York State (Danforth & Magnacca 2002). Andrena are much more common in temperate than tropical regions (Michener 1994). Over a quarter of the bee species in the Northwest United States are in the genus Andrena!

Floral relationships: In the western United States, Andrena are among the most common bees that forage in the Spring. Some species emerge as early as March or April. The genus contains both generalist and specialist species, the latter whose form and structure are often adapted to particular flowers (Michener 2000). Some plant taxa, such as Camissonia, are highly dependent on Andrena for pollination. Many Andrena forage mainly during twilight hours, but some forage pre-dawn or early morning (Stephen et al 1969).

Nesting habits: Most Andrena are solitary nesters, and they often nest in large aggregations. A few species nest communally, where two or more females share a nest but build and provision their own nest cells. All Andrena nest in the ground; they often prefer sandy soil near or under shrubs. Brood cells are lined with a waxy material secreted by the female (Michener 2000).

Diagnostic characters: Andrena have a variety of striking colorations but species are difficult to tell apart from each other (Michener 2000). In general, North American species are small to medium bees (0.3 to 0.7 inches) that are black or dull metallic blue or green. Most species are moderately hairy and have pale bands of hair on their abdomen (Michener 1994). Females have large, velvety facial foveae (depressions) and large scopa (brushes of hairs for holding pollen) on the upper part of their leg, seemingly in their “armpits”.

Similar taxa:

Known conservation concerns:Two Andrena species are listed as Vulnerable on the Xerces Society’s Red List of Pollinator Insects, and little is known about their biology. Both have limited ranges that may be threatened by habitat loss. Andrena aculeata is endemic to the Columbia River Basin in the Northwest. Andrena winnemuccana has only been collected once within its only habitat, Wyoming sagebrush in the Columbia River Basin (Shepherd 2005).

Interesting fact:

Additional resources: Michener & Rettenmeyer (1956).

World map of the species of Andrena

Key to Eastern Andrena females at DiscoverLife

Key to Eastern Andrena males at DiscoverLife