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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

Andrena-with-worn-wings
This Andrena has worn wings, but the scopae on her rear legs are clearly visible. © Rusty Burlew.
Andrena-in-bark
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.
Andrena-in-flight
This bee is flying toward her nesting hole. Notice the pollen packed between thorax and abdomen. © Rusty Burlew.
Andrena-pygidial-plate
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.
Andrena-in-hole
An Andrena female peering from the mouth of a tunnel with a small tumulus built around the edge.

Comments

Mark
Reply

Cool indeed!

Muddyvalley
Reply

Very interesting & great shots! What do you use for your lighting setup?

Rusty
Reply

The sun.

Anna
Reply

Last Saturday a bug-killer showed up at our door offering to spray for bugs like stink bugs and BEES. Thankfully for him, my husband answered the door, because if I had…

Anyway, my neighbor’s back yard is a parched desert, I noticed all these holes and insects flying just above the holes as I walked across to retrieve my son’s ball. I stopped to take a closer look and there were hundreds of them, all flying very low. Suddenly one slowed down enough that I could see it was a very fuzzy, gray-looking bee. Actually, it was what I had thought a few weeks ago was a leaf-cutter bee, but it was NOT a leaf-cutter bee, I think it’s a mining bee. I hurriedly shot off an email to my neighbor as I remembered that bug-killer visit and he returned a very reassuring reply. No bug-killers planned but maybe some grass and watering in the fall to discourage such mass nesting. He was grateful for my confirmation that they were harmless.

Disaster averted plus he wanted to make sure my bees weren’t affected by his! I love my neighbors. Sorry for the long comment, but your post reminded me of this.

Rusty
Reply

Anna,

Isn’t it exciting when you start knowing what they are? I get all worked up just reading this stuff. And every time I hear a story about disaster averted, I start to believe that all this work is worth it. Thanks for writing!

Glen Buschmann
Reply

Thanks Rusty
Enjoyable and informative, then and now. Seeing your photos I am more appreciative of watching only their hind ends as they vanish down the holes.
Glen

Andrew Hogg
Reply

Damn I love you Rusty! You’re such a bee nerd!

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