Andrena mining bees

About a week ago, my friend Glen asked if I wanted to see an underground aggregation of bees. Of course I did! I was elated, so armed with a backpack full of camera equipment, I went to meet him at an Olympia residence.

First, he showed me the holes. Entrance holes lined the driveway/lawn interface, some were dug into the soil beneath the shrubbery, and others opened beneath landscape timbers. A scattered few had tumuli—mounds of soil surrounding the entrance. We didn’t see any bees right away so I began to worry that it was past their season. But soon they begin to appear.

After a look through the camera lens, I was pretty sure they were in the genus Andrena. This is a large genus of short-tongued bees, comprising about 1300 species. They are most often black (although other colors exist) and often the abdomen appears shiny, even though it has bands of hair. Although the Andrena bees are hard to tell apart, it is fairly easy to distinguish the genus itself. Here are four things to look for:

1. Most have deep facial foveae (depressions between the eyes and antennae) covered with dense hairs that look like velvet. I’ve been told that those patches are unique to the Andrena and so can be used to identify the genus.
2. Andrena also have propodial corbiculae. Say what? The propodeum is the first abdominal segment, the one that is attached to the thorax. Female Andrena have long, dense hairs on the back and sides of the propodeum which are used to transport pollen. Translated, propodial corbiculae are just pollen baskets in the space between the thorax and the abdomen. They are often referred to as “saddle bags.”
3. Also obvious in the female Andrena bees are extremely long hairs on the hind legs—also for collecting pollen. These hairy areas are called scopae and can hold lots of fluffy pollen.
4. In many species, the pygidial plate is visible in the female. This is a triangular area at the end of the abdomen that is used like a spatula to spread the waterproof secretions she uses to protect her nest.

Three or four days after I took the photos, I spotted the same type of bees at home on a high-bush cranberry. I’ve never seen bees of any type on this plant, but this year it’s covered with these pretty black Andrena bees. I’ve never seen their nesting holes, however, so I have no clue where they are living. But still, so cool.

Rusty
HoneyBeeSuite

This Andrena has worn wings, but the scopae on her rear legs are clearly visible. © Rusty Burlew.

See how much pollen her hairy legs can carry? Also notice the hair in the facial depressions. This bee is crawling through bark mulch to get to her entrance hole. © Rusty Burlew.

This bee is flying toward her nesting hole. Notice the pollen packed between thorax and abdomen. © Rusty Burlew.

The pygidial plate is modified from the last visible abdominal segment. She uses it to smear waterproof secretions on the inside walls of her tunnels. © Rusty Burlew.

An Andrena female peering from the mouth of a tunnel with a small tumulus built around the edge.