Researchers in Ontario, Canada, studied the qualities of artificial domiciles, or nest boxes, for bumble bees that will successfully attract colonies to nest in them. Above-ground nests, such as this one attached to a tree, were the most-used kind in the study, though still at a low percentage, with colonies using just 13 percent of the boxes placed in the course of the study. (Image originally published in Johnson et al 2019, Journal of Insect Science)

By Meredith Swett Walker

Bumble bees aren’t hard to spot. They’re relatively large, charismatic balls of buzz and fuzz. Their nests, on the other hand, can be pretty inconspicuous. Bumble bee colonies are relatively small (at most a few hundred individuals), so they produce a lot less traffic than a honey bee colony, which may contain tens of thousands of bees. And nests are often built underground in old rodent burrows or concealed in dense grass tufts or small tree cavities. These hard-to-find nests make it hard to study the nesting ecology of these important pollinators, many of which are exhibiting alarming population declines.

Meredith Swett Walker

But artificial nest boxes—or bumble bee “domiciles”—just might make studying the nesting ecology of these wild bees easier. For instance, ornithologists know much more about the nesting biology of bluebirds than meadowlarks because the former can be convinced to nest in convenient, easy-to-access nest boxes, while the latter constructs well-hidden nests on the ground in grasslands. The question is, can you get wild bumble bees to use domiciles?

In a paper published in January in the Journal of Insect Science, Sarah Johnson, a Ph.D. student at Simon Fraser University, along with colleagues from Wildlife Preservation Canada, York University, and the University of Guelph, compare three different installation methods for bumble bee domiciles to see which is most successful. In addition, the researchers compared the diversity of bumble bee species using the domiciles to species diversity assessed with traditional netting surveys to determine if certain species were more likely to use domiciles than others.

The researchers installed 346 bumble bee domiciles across 15 sites in south central Ontario. The domiciles all had a similar design: essentially a plywood box lined with raw upholsters’ cotton, with a small entrance hole, and with plastic sheeting covering the lid to aid in weatherproofing. Some domiciles were affixed to tree trunks (above-ground installation), while others were buried underground (underground installation) or under piles of vegetation (false-underground installation.) Underground and false-underground domiciles had a length of narrow PVC pipe affixed to the entrance hole to serve as an entrance tunnel.

Researchers in Ontario, Canada, studied the qualities of artificial domiciles, or nest boxes, for bumble bees that will successfully attract colonies to nest in them. Just 4 percent of underground nest boxes such as this one were inhabited by bumble bee colonies in the course of the study. Researchers speculate these boxes may have had problems with drainage or entrance blockage that made them unattractive to their potential inhabitants. (Image originally published in Johnson et al 2019, Journal of Insect Science)

Researchers in Ontario, Canada, studied the qualities of artificial domiciles, or nest boxes, for bumble bees that will successfully attract colonies to nest in them. None of the “false-underground” nest boxes such as this one, placed under brush or leaf litter, were inhabited by bumble bee colonies in the course of the study. Researchers speculate these boxes may have had problems with drainage or entrance blockage that made them unattractive to their potential inhabitants. (Image originally published in Johnson et al 2019, Journal of Insect Science)

The researchers then visited the domiciles (but did not open them) during the summer to check for nesting activity and conducted netting surveys to determine number of species and abundance of bumble bee queens at each study site. At the end of the nesting season, domiciles were removed and opened to determine if they had been occupied and by which species, as well as the size of the colony.

Overall, only a small number of the domiciles were used by bumble bees. Just 13.3 percent of above-ground domiciles and 4.1 percent of underground domiciles were occupied, and none of the false-underground domiciles were used. The researchers speculate that the underground and false-underground domiciles may have had problems with drainage and that their entrance tunnels were frequently blocked by vegetation.

Six different species of bumble bee nested in the domiciles, even some species that were relatively rare based on the numbers of queens caught during the netting surveys. This means that, even though domicile occupancy rates were low, the species that used the domiciles gave a fair representation of the species richness of the bumble bee community in the area. However, some species, such as Bombus perplexus, seemed to be more likely to use domiciles than other species, such as Bombus impatiens.

Johnson said one of the biggest surprises in this project was finding a large colony of Bombus ternarius, or tricolored bumble bees, in a domicile where no external indications of nesting activity had been observed during visits—a testament to how hard nests can be to detect. “I counted over 800 individual cells that once contained bee larvae, which is quite large for a bumble bee colony of any species,” says Johnson. “The fact that there were no external signs of bees when we checked on that domicile was intriguing, and we suspect this likely indicates a strong species-specific life-cycle timing, so we just missed the peak period of activity when we looked. For me, observations like this really drive home the potential of these domiciles for use in studying bumble bee colony development in the field.”

In a study on the usage of artificial nest boxes for bumble bees in Ontario, researchers saw no external indications of nesting activity by tricolored bumble bees (Bombus ternarius,) but were then surprised to find a colony of nearly 800 had used one of the boxes when it was examined at the end of the study—a testament, researchers say, to how hard bumble bee nests can be to detect. (Photo credit: David Cappaert, Bugwood.org)

Two Bombus perplexus workers peek out of an above-ground domicile. (Photo credit: Sarah Johnson)

Johnson and her co-authors conclude that domiciles could indeed be a useful tool for studying bumble bee nesting ecology if occupancy rates can be increased. She notes that colleagues at the University of Calgary have had much higher occupancy rates in their domicile study (as yet unpublished), and she suspects that how and where the domicile is installed is key to increasing occupancy. But, even after working with bumble bee domiciles for a few years, she says installing them just the right way, in just the right spot, “feels like more of an art than a science.” Johnson and co-authors say more quantitative evaluation of installation methods and other factors is needed.

Want to Build Your Own Bumble Bee Nest Box?

If you are interested in trying a bumble bee domicile in your yard, Johnson has some tips. Many domicile building plans are available online, including this bumble bee domicile building plan from the University of Nebraska-Lincoln Entomology Department. Johnson recommends the above-ground installation method: “strapped to a tree or fencepost or even placed on the surface of the ground, hidden in a bush or in vegetation or leaf litter.” Domiciles should be installed in early spring, and waterproofing the lid or roof with plastic sheeting or another material is key. Finding the right spot can be tricky, but Johnson successfully used a new strategy when placing a domicile in her yard. “In early spring when you start to see a lot of big buzzing queens coming out of hibernation and searching for nest locations, go out and sit in your yard and just observe them. The queens will show you what they’re interested in—they often search along edges, like along your fence or along the side of a staircase or the edge of a deck. They might spend time digging around in an old wood pile or around a garden shed. When you notice that type of interest, put a domicile there!”

Meredith Swett Walker is a former avian endocrinologist and wannabe entomologist. She now studies the development and behavior of two juvenile humans in the high desert of western Colorado. When she is not handling her research subjects, she writes about science and nature. Find a sampling of her work at www.magpiescicomm.com.