Encouraging Native Bees in the Garden
Last night I went to a lecture by Professor Gordon Frankie (UC Berkeley) on encouraging native bees in urban gardens. It was a really interesting talk, and while I knew some parts of it (the bits about mulch came up during some earlier reading on native plants and plantings), much of it was new and interesting. Here's my summary of the lecture:
There's more interest in native bees now that the problems with managed honey bees have become more acute. But the biggest problem for native bees is the loss of habitat to development and agriculture.
I did not realize quite how many native bees we have in this country. In the US there are about 4,000 species of native bees (not including Apis mellifera, the European honeybee, which is obviously not a native with that name). None of them produce commercially viable amounts of honey. 1,600 of those species are in California, and in Berkeley alone they have found 82 species and expect to be able to find more than a hundred eventually. Frankie has a test garden in Berkeley that has attracted 37 species of bees with a mix of 100 types of plants (not clear whether this was species or varieties).
Some of the bees are really weensy: there was a display of several species from Sacramento and while most bees were what I think of as "normal bee sized," plenty were small enough to look like flies or gnats. As we were looking at the case, a woman near me gasped that she had probably been killing bees for years without knowing they were bees rather than flies.
Different kinds of bees have different emergence patterns. So a bee might only come out in the early spring, mid-spring, summer, or late summer, and not be seen at any other time. One of our more common native bees, the ultra-green bee, can be around at all seasons in various parts of California.
If you know anything about native pollinators, you probably know that many of them are solitary, unlike honey bees. But they live close to each other and some of them, after competing all day for food and mates, will fall asleep in close proximity to each other.
The most fascinating new fact for me was that deserts are really great places for bees. Apparently there are about 400 species of bees at the Pinnacles. Interestingly enough, the best city for bees in California is Santa Cruz, because of the widely varied garden styles. Berkeley is a distant second place. Paso Robles is horrible, because most of the landscaping is dead lawns and privet -- Frankie and his team simply stopped trying to do bee counts there.
Places where a lot of houses use lawn/garden services are bad, too, because of the plant choices those services tend to offer.
A variety of plants in a garden is important to attract bees. Particular bees pollinate specific types of flowers, and those alone, but they are attracted to a site by a variety of plants in sizable patches (Frankie suggested 1.5 meter square as a good size for attracting enough bees to do research) near each other. Interestingly, the same bees will be on the same plants all over the state, no matter where those plants are. They tend to like white, pink, purple, blue, and yellow flowers, with very little crossing over to the reds and oranges.
Native bees also prefer native plants. While they will visit non-natives, they are attracted to sites with natives and to the natives above all else. Their favourite plants are from the Asteraceae, Lamiaceae, and Polygonaceae families, which are asters, mints, and buckwheats to you and me.
Native American food plants like squashes and tomatoes are pollinated by native bees. And hey! It turns out that honey bees don't pollinate tomatoes at all. Tomato flowers need what is called "buzz pollination" where the flower is shaken, so bumble bees do the pollination. I had seen bumble bees being used in greenhouses full of tomatoes, but I assumed it was because they were a bit more manageable than a hive full of honey bees in that situation.
For nesting sites, 70% of our native bees nest in the ground. They are very good diggers, and the nests tolerate being walked on just fine. But they don't deal well with deep mulching, and do best with patches of bare soil -- habitat loss being a major problem for native bees, this is a big issue. I imagine lawns are not great for them, either.
Various bees prefer different types of soil, so there's no need to try to change that drastically to attract them. One suggestion I found interesting was that many bees would like a small-ish berm (maybe 10-12 inches high) to nest in -- they burrow into the side -- so you could kind of build one of those into your garden design. Other suggestions were large chunks of wood with holes of various sizes (3/16", 1/4", and 5/16") drilled 3-4 inches deep to allow nesting spaces for several species of bee who prefer nesting in holes. But when you provide such a nest you have to take care of it (shelter from sun and rain, clean out the holes to prevent mites, etc.).
One person in the audience asked what to do when your nesting block was taken over by other, less desirable bugs (wasps, or a type of bee you did not want to encourage for some reason). The answer was to provide more blocks to reduce competition for the space. I loved the simplicity of that approach: don't try to control the competition or the mix of insects on your site. Just invite them all in.
If your greatest fear in attracting these bees is stinging, you should know that bees are generally afraid of humans and will stay out of your way (Frankie suggested getting low to the ground and not moving too much if you want to observe them on a plant). Unlike honey bees, these bees do not die when they sting (probably because they are solitary and dying whenever you stung would kind of limit reproduction). Only the females sting, though that is not much of a consolation.
During the lecture, Frankie mentioned several useful plants for attracting bees, but probably more useful than my list of those varieties is a link to his more complete list of bee-friendly plants. There's a ton more information on the rest of his site, too.
My take-aways from the lecture will be to make larger patches of the plants I have. The plant-collector approach is fun but not great for the kinds of insects I want to attract. I will also spend some time clearing out patches of space for nesting sites, and maybe build a better berm (there's a small one alongside the neighbor's cottage, and bees already nest there, but I could extend it). My current approach of trying to remove as much Bermuda grass as possible seems to be a good idea. I will take some suggestions from the plant list and use them for building out sections of the garden. I may also try making some more nesting blocks, though just putting the ones I have out in the garden would be a nice thing.
posted by ayse on 02/05/08