by: Morris Lemire and Hal Hopkins
Bees are essential to our gardens and to our food. Without bees to pollinate crops there would be less variety and fewer nutritional foods available. As it happens, local indigenous bees are the most efficient pollinators of all, so it makes perfect sense to give them all the help we can.
A group of gardeners from U of A south campus first met in February 2015 to discuss issues around pollination, companion planting and flowering perennials. Included in this group are: Hal Hopkins, with Green & Gold Community Garden (who has done most of the field research for this project), Morris Lemire with Edmonton Organic Gardeners Guild (EOGG), and Michael Granzow who is at Prairie Urban Farm. Our focus on native bees and their nesting habits grew out Hal’s early work, our first meeting, and Sustainable Food Edmonton’s bee log initiative of spring 2015. Since May 2015, we have monitored and collected data from six different kinds of nesting boxes, including SFE’s bee log.
Bees are widely written about, more so than most other insects, but it is the introduced European honeybee that gets the lion’s share of attention. In second place are our domestic bumblebees, mainly because they are large and easily seen. In third place is the hybridized African bee, the so-called “killer” bee, because it is a story that the press has sensationalized.
Way down the bee list are our native solitary bees. They are usually not noticed because they can look like small flies, wasps, or flying ants. Further more, unlike the three bees mentioned above, they don’t sting, so we tend to ignore them: no threat, no respect. But getting to know them, giving them a helping hand is one of the best things you can do for your garden.
Many of our wild native bees are homebodies; they forage for pollen within a radius of 50 meters to a few hundred meters, as opposed to honeybees, which forage out to a radius of several kilometers. This means if you provide local solitary bees with flowering plants during the growing season, along with nesting sites where their larva can over winter, they will stay very close to your garden and be there in the spring when you need them. By providing them with flowers and nests you can increase their numbers within the vicinity of your garden. And because they are very active pollinators, possibly visiting up to 1875 blossoms a day, they are the quintessential gardener’s friends. Simply put, you can boost pollination, and therefore your crop yields, by encouraging solitary bees to visit your garden and to hang around.
Nesting habitat varies with different types of bees. Some are ground nesters like the burrowing sweat bee, or bumble bees, which use abandon mice and snake holes. Others nest above ground in crevasses, rotten wood and hollow reeds. It is the above ground ones that we are after, such as the mason bees and leafcutter bees. Their first task is to mate and then find a suitable hollow to start a nest. In the case of Mason bees these tunnels are separated into individual cells and sealed with mud hence their name. Leafcutter bees use bits of cut leaf to line and section off the larger nesting space into these smaller cells. The female prepares the cell for her offspring by gathering and depositing pollen and nectar in the cell. When she has gathered a small wad she lays an egg on it. Then she walls off the cell and starts a new one. These cells are about two centimeters long, depending on the size of the bee. The total number of cells depends on the size of the cavity. When the egg hatches, the larva feeds on the stored wad of pollen and nectar. The next stage is pupation, then metamorphosis, resulting in a winged adult. The first egg deposited in the deep end of the cavity, where it is safer, is usually a female, followed by a series of males. The males emerge first, in succession, chewing their way out of their nesting cell, defending the nest and awaiting the female. Thus the cycle begins anew.
Building a nesting box for solitary bees is easy, fun and informative. The tricky bit is getting the diameter of the nesting holes just right and, of course, we’ll give you exact dimensions based on our trial and error. These are the details that most commercial bee houses get wrong, especially for the native bees in our area. One size does not fit all. Usually the holes are too large. We have tried them and the success rate was extremely low.
There are two basic parts to a human built bee-nesting box, the outer housing, or at least a roof, and the material that you will put into it. These inserts, wooden blocks and/or plant tubes, contain the actual holes in which the bee will construct a cell, in which they lay one egg per cell. The actual box can be made from any scrap lumber, as long as it is untreated wood. In one case we used a wooden wine box. Ask your local fine wine shop if they will save you one. This exterior wall should be rain proof with an overhanging eave in the front. We recommend keeping the box on the small side, no larger than a wine box. The larger your housing the more material you will need to fill it, the heavier it will become and consequently, all the more difficult to mount securely.
Locate your nesting box facing south; bees are cold blooded and use the sun for warmth. It is important to provide water close to the nest, as well as some fresh, soft mud; keep it moist. Make very sure your box is well anchored so that cats, crows and other curious creatures can’t jar the box, or worse, knock it off entirely. You must secure the nesting holes (blocks and tubes) by bundling them together and then tying the bundle to the floor or sidewall. Otherwise, magpies or squirrels will climb onto the box and fling out the nesting material just for the sheer fun of it. This can result in the egg being knocked off the feeding wad.
The native bees in question are very particular about the size of their nesting hole, preferring a snug fit. Since most of our local bees are small, we found that any diameter over 6.5mm, or a 1/4“, was too large for the above ground, wild native bees in our area. As for length, the rule of thumb for holes under 6.5mm (1/4“) in diameter is 50mm to about 100mm (2“- 4“), or conveniently, the length of an average drill bit.
The tubes we used from plant materials, such as lovage, dry rhubarb stalks, dried delphinium stalks and elderberry, were not nearly as effective as the smaller holes we drilled into wooden blocks. To be honest, we found that plant tubes were a lot of work. You have to harvest them, cut them, clean out the inside, all of which takes more time than you might think. For example, if you use elderberry, you will have to drill out the soft center and assure that the hole is clean and free of sharp barbs. Rhubarb, lovage and delphinium have a hollow core, but believe us when we say it’s not easy to find material with the small holes we will recommend.
As for the actual wooden block, it can be a scrap end of 2 x 4, or a section of log. Avoid pressure treated lumber or anything soaked in creosote. It is faster and easier to drill the holes using a drill press, but if you don’t have one, a hand-held electric drill will do just fine. If you are using a hand held drill, space the holes wider apart to prevent any two holes from intersecting. Here’s a neat tip; use a paper template to space and mark where you will drill your holes. This makes it easier to drill them parallel to each other. Another important detail of these holes is that the entrance must be free of slivers.
This is the point in the project where attention to detail is crucial. Here’s what we know for sure. We drilled test blocks using every bit in Hal’s kit, from 1/16“ to 3/8“, in 1/64“ increments (1.5mm). The most popular series of holes used by the bees that we got in the test blocks were, 7/64“ (2.5mm), 11/64“ (5mm) and ¼“ (6.5mm). The data from the other houses showed that the common drill sizes, 1/8“ (3mm) and 3/16“ (4mm), will suffice.
Obviously, the big advantage with the block method is that you get to choose the bit size right from the start. You can also use your drill kit for measuring the diameter of holes in natural stock. So while we would still suggest a mix between reed and block, our test results showed that local bees preferred the blocks by a ratio of 10 to 1.
Concerning the five different bees that used our test sites, we have identified two and are still working on identifying the remaining three. One that we believe we have possibly identified is an Osmia nigriventris, generally known as a mason bee. The other is Hylaeus sp., or a Yellow-faced bee. We are pretty sure that one of the yet unidentified bees is a leafcutter, Megachile sp., because it capped its nesting hole using leaf pieces. Hunting down these facts is – how best to put it? – entertaining? We wish you all the best.
There are around 370 different species of native bees in Alberta, so it is very tricky to say exactly which ones are in which area. Therefore, we would caution that what is true for our area may not be true for another part of the greater Edmonton area. We have seen some differences between Hal’s country site, 150 km west of Edmonton, and the gardens in the city on U of A’s south campus farm. Different habitat (vegetation, ground cover, soil and water) will attract different species of wild bees. With keen observation you will learn what is around after you put up your bee box. Indigenous bees, along with other pollinators, are in decline throughout North America. You can help protect indigenous populations by enhancing habitat, providing nesting opportunities, avoiding pesticides and creatively working with your local environment.
In summation, we don’t see nesting boxes for solitary bees as a substitute for companion planting or planting flowering perennials that bees love, such as dandelions, elderberry and chives. Rather they should be seen as contributing to a healthy garden, plant diversity and pollination in general.