Digging in the garden

garden

Inspired by the bounty of fresh produce picked up through our CSA last year, as well as the convenience of a few different veggies such as lettuce or peas being grown in our landlady’s veggie garden (she said we could help ourselves; she wouldn’t be collecting it all), I’m planting the garden again this year with a variety of items. I started many of the seeds early, indoors, and have just recently been getting coordinated enough to transfer the hardy stuff outdoors, as well as plant the cold-tolerant items. First things first: I had to get a fence up around the perimeter of the 350 sq ft space – not so much to keep the deer or rabbits out (we had no trouble with either last summer) as the dog (who doesn’t stop her mad gallop where the trail ends, and is happy to dig, too, if you are). It took a while to find the time to get this done, as it required a full afternoon. Finally, the fences went up last week, using odds and ends we found around the sheds. With the perimeter established, I could move on to the actual ground prep.

Mining bee

The delay in getting started allowed some other critters to take up residence first. As soon as the ground had thawed out and was warm enough to dig in, I started seeing bees buzzing about the sandy plot, low to the ground. I knew what they were, from having encountered something similar last spring: they’re mining bees, family Andrenidae, probably genus Andrena. Although there are many different species of mining bee, which will fly at different times of the year, most of this genus are active in the spring.

Mining bee burrow

Probably most or all of the bees in the garden plot are females, busy working on nest sites. The bees are solitary, meaning each female builds her own nest without help of others, and provisions it herself. The fact that there were literally dozens of them in this small area is simply because they need exposed soil in order to start digging their nest. This doesn’t have to be a large expanse; I saw a few bees digging in tiny thumb-sized bits of dirt out in our lawn, too. But the garden, having very little vegetation, was really an ideal location. The female bees pick out a spot and start digging tiny tunnels into the soil. These are usually branching, and each branch ends in a small chamber where the female lays an egg.

Mining bee

She’ll then provision the egg (or, more accurately, the larva, once it hatches) with pollen and nectar that she’s collected up from spring wildflowers. You can see all the pollen clinging to the hairs on the legs of this bee as she heads back to the burrow she’s dug. She may need to make many trips to fully provision her burrows. Once a cell has both egg and pollen she’ll close it off, and the larva is left to develop on its own over the summer.

Mining bee

At one point, as I was sitting and waiting for somebody to land and stay still long enough for me to take a photo or two, one bee swooped down and landed on the one I was stalking. I only got one quick, blurry photo, unfortunately, so it wasn’t completely clear what was going on here. A male arriving to mate with a female? One female expressing displeasure at the presence of another? Disputing a land claim, perhaps?

Mining bee

Unfortunately, I needed to rake out the ground to prepare it for planting. Weeds had grown up since the end of the last growing season, and the earth needed to be loosened a bit after the packing from the winter snow. I was terribly reluctant to dig up all these burrows the poor bees put so much work into, but really didn’t have any option about it. They’re very docile bees, however, and I found I could wander about the garden setting up the fence and, later, starting to work the ground without them getting too worked up about it.

Solitary bees and wasps find their burrows using landmarks such as twigs or tufts of grass, and if these are removed or moved they become completely disoriented. A lot of the buzzing about I observed (before working the soil) was the bees arriving and looking for their landmarks to orient themselves to their burrow. I felt very badly for raking over all their hard work, and it was sad to see them come back and zig-zag back and forth over the area where their burrow used to be, looking for the landmarks that I’d since removed. I think, however, at least some of them started new burrows since I found fresh holes in the raked soil the following day. Next year I’ll have to go out and get the garden prepared earlier in the season so they can start their digging after I’m already done.

Bees of the earth

Mining bee

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.

Mining bee

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.

Mining bee

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.

Mining bee

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.

Mining bee

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.