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The accidental pollinator garden, part 1: bare dirt for bees

A grizzled gray and white digger bee female with dark eyes emerges from moist, bare ground
Digger Bee - Genus Anthophora

When my family moved into our house, we noticed that our yard was scruffy compared to the neatly manicured gardens in the rest of the neighborhood. Not just scruffy; mangy. The flowers were beautiful but unkempt, and there were many patches of dirt left bare, without even wood chips covering them. Because I’m a hopeless gardener, the yard stayed that way. But it ended up being a blessing in disguise by serving as a perfect ground-nesting bee habitat. If you are as lazy as me, then you, too, can attract native bees to your yard!

The yard is on a south-facing slope, so we get a lot of light and stay a few degrees warmer than the ambient area. As I described in a previous post, I first noticed Halictus rubicundus late last summer nesting in the flattest areas of bare sandy dirt in my yard. To my great pleasure, since then I have discovered that each of the several types of dirt in the yard has attracted its own set of bee species.

Early this spring, I noticed a large aggregation of Anthophora nesting on an area of sloped, loose-packed sandy dirt between large rocks. These large bees are beautiful, with fuzzy white stripes on the females and fetlock-like leg tufts on the males. I was especially glad to be able to observe a nesting site, because while some bees linger obliviously on flowers for the benefit of photographers, the Anthophora are extremely fast and maneuverable and are easy to startle. Instead of having to chase them as they foraged, I was able to camp out by the site each morning during the couple of weeks when they were emerging. Each bee would poke its head out, slowly creep a little further, sit in the sun to warm up, and clean the dirt off itself. Some of them even slowly rotated, showing me themselves from a range of angles. Each bee would fly off after a few minutes, forever escaping beyond the range of my photography skills. But I had plenty of chances because there were plenty of bees; at one point I counted 59 holes, each likely containing multiple nest cells. For a few weeks, the males buzzed energetically around the nest site, sparring with each other and looking for new females to mate with. Now, with only pollen-laden females efficiently coming and going, the aggregation is much quieter.

A female Anthophora digger bee peeks out of a nest hole in bare dirt
Female Digger Bee (Anthophora sp.)

A few weeks later, bees in the genus Andrena started to emerge. These small, fine bees spent several days flying around and sunning themselves on the leaves of bushes in the hard-packed, less-sandy area. I eventually noticed that they had started to nest in the dirt there, sometimes leaving small mounds of excavated dirt around their exposed small holes, and sometimes hiding their nest entrances under plant matter.

The nest entrance of a mining bee, Andrena sp., in bare dirt with tailings surrounding it, under fallen flowers.
Andrena nest hole
A male Andrena mining bee on winter heath flowers
Andrena (male)

Next, the wave of cleptoparasitic bees showed up. Where there had been a cloud of Andrea, there were now many striking red, nearly hairless Nomada. These bees hover delicately, methodically exploring the ground and poking their heads into nest holes. Like the Andrena, they pause photogenically on leaves.

A red nomada bee prowling on the bare ground
Nomada sp.

I noticed Sphecodes, cleptoparasites of Halictus, showing up around the same time. In contrast to the Nomada, the Sphecodes skitter jerkily between nest holes, often climbing all the way in to investigate.

A female sphecodes bee with black head and thorax and red abdomen prowls the bare dirt
Sphecodes sp.

To my surprise, there then came yet another wave of new something-or-others. They were tiny, they were black, they had fearsome-looking mandibles, they were ducking in and out of both the large Anthophora holes and tiny (2mm) holes interspersed among them, and they were zipping around so fast that I found them extremely difficult to photograph at all. That was the push I needed to finally learn to use trigger-priority mode on my camera. With that new skill plus some patience, I got photos that were good enough to convince me this was something I’d never seen before. A fellow WaNBS member kindly ID'd them for me on iNaturalist as Panurginus, a genus in the family Andrenidae. The zippy bees were probably males desperately seeking females. On a cooler day, they were moving more slowly and I managed to get some photos of them mating.

Two black Panurginus bees mating on bare dirt
Panurginus sp. (mating)

Lasioglossum ovaliceps is a beautiful bee similar to Sphecodes in coloration but with a longer head and a pollen-collecting rather than a cleptoparasitic lifestyle. I’d seen them on flowers last year, but I’d never managed to find their nest holes. I finally spotted one going into a tiny hole right in my yard, in a rough vertical wall of large rocks with well-drained, loose sandy dirt between them.

A dark gray bee with red abdomen on a leaf, Lasioglossum ovaliceps
Lasioglossum ovaliceps

If you, too, are a lackadaisical but bee-loving gardener, I suggest you try establishing ground-nesting bee habitat yourself. Pick a sunny, well-drained spot and clear it or leave it bare. Let us know if something cool moves in!

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