About a week ago I took Raven up the road to the abandoned property for her daily walk. It was a gorgeous day, and as I’ve done on most gorgeous days recently, I took my macro lens and kept an eye on the ground looking for bugs. I’m starting to see a lot more insect activity on the warm days, particularly on sunny afternoons, and especially on south-facing slopes in open clearings. There are two such south-facing slopes at the property, and I make sure to pause and scan them at least once on every visit now.
On that particular day, I happened to notice some new activity at one of these sites. Insects, flying low to the ground, near a bit of bank where there was no leaf litter so the soil was exposed. The slower, winding flight of the insects, along with their weaving back and forth as they prepared to set down on the ground, made me think these were bees, and indeed as I got closer I was able to snatch a quick look at a couple before they popped into the air again, confirming the ID. Beyond that rather broad classification, however, I wasn’t sure what I was looking at. My mind thought immediately of a post about long-horned bees that I had read over at Bug Eric‘s blog recently, but although these bees had longer antennae, their behaviour didn’t seem to fit.
I settled down on my knees in the dirt in front of the bank and waited, hoping for one of them to come to rest on a leaf near enough to me to be able to get a few photos, in part to help with identification later, but also to share on the blog. As I waited patiently (Raven, also; she had found herself a nicely destructable stick), I happened to notice this bee inside a little hole in the dirt. Figuring it would likely be leaving shortly, I set my camera pointed at the hole and waited. The bee seemed to be taking its time. I couldn’t really see what it was doing, as the hole was too small to get a good look.
Finally, after a few minutes of sitting with the camera pointed at the hole, the bee emerged. I got a couple of shots and then it took off. Curious, I took a twig and started poking around in the hole. My hypothesis was that these were young bees emerging from the burrows where they pupated and turned into adults. I was expecting that if I dug around a bit I might be able to find more of them, but there was no evidence of any other bees, or even any burrows of any sort. Puzzled, I left the bees to their activities, gathered up Raven and headed home.
It was only when I got home and cracked open my Kaufman guide to Insects that I figured out the answer. These were mining bees, members of the family Andrenidae. They are solitary bees (as opposed to the colonial sort we think of traditionally with honeybees), who build nests in the ground into which they deposit their eggs. So they were in fact building burrows, not leaving them. I felt badly for having destroyed that poor female’s hard work.
They tend to nest in loose congregations, however each female bee builds her own nest by herself, and the proximity to other nests is mostly a function of habitat availability. They typically create a network of burrows, with the entrance often under a leaf or the edge of a log or rock. At the end of each burrow the create a nest chamber into which they place a ball of pollen and nectar collected from local spring wildflowers, and they lay their egg on this ball. When the larva hatches out, this is what it feeds on until it is ready to pupate. The female seals off the chambers once the egg is laid, and the young are left to fend for themselves.
There are several genera of mining bees; I believe these ones belong to the genus Andrena, although identifying them down to species can be difficult and usually requires an expert, which I am not. Most mining bees in the genus Andrena are springtime fliers, although there are some that are out and about in summer or fall, and a handful even in winter (probably not up here, though).
They continue to hang out at that same spot, I noticed them again last time I took Raven there, though I didn’t spend any time watching them. They only raise one brood per year, so once these eggs are laid, the adults will all die and disappear, until the new generation emerges next spring.