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I never would have spotted this small carpenter bee if the northern crab spider hadn’t grabbed her and held her still for me! These small bees build their nest in hollow plant stems. Photos by Emily Stone.
The activity of bumble bees in the museum’s pollinator gardens has continued to distract me through my office windows on warm afternoons. But bumble bees aren’t the only bees out there; the other bees are just hidden.
Of the 166 species of bees who are native to Northwestern Wisconsin, approximately 70% nest in the ground, and 30% nest in tiny holes in wood, hollow twigs and stems, or other above-the-ground cavities.
While bumble bees are part of that first group, little cuties like blue orchard mason bees, small carpenter bees and masked bees don’t have the large body size and warm fuzz that allow bumble bees to fly in cooler temperatures. They may already be snuggled cozily into burrows or hollow stems hidden in the garden…
...Or wish they were. On last week’s hike when I spotted dozens of bumble bees, I also snapped photos of a metallic green small carpenter bee in the clutches of a northern crab spider. She was likely a mother bee who had spent the summer laying and provisioning eggs in a hollow stem, and then standing guard at the nest entrance to ward off parasites.
Even with her vigilance against invaders, the survival of her children and grandchildren truly depends on hollow plant stems left standing after they die. And this is where gardeners can help.
In the warm, dry, mosquito-free afternoons of autumn, it’s tempting to look for ways to stay outside longer. Often that means “cleaning up” the gardens. I’ll tear out my tomatoes, clear the bean vines off the trellis, and make sure that there is no disease-carrying residue left in my plot.
In your flower gardens, though, especially if you’ve planted native, perennial species with the bees and butterflies in mind, it’s best to leave the flower stalks alone.
As I was cleaning up my plot in the Cable Community Farm last week, I paused to chat with a volunteer taking care of the pollinator plantings around the edge. She was carefully snipping off bergamot stems in order to get at the weeds more easily.
We chatted for a minute about the best ways to support pollinators, and I reminded her that many bees need these stems for nesting.
The time to cut back your dead flower stalks is early spring, just before bees begin to look for new nest sites.
“But I’ve been working with flowers all my life,” she expressed in confusion, “and I’ve never seen any signs of a bee nesting in any of the stems!”
I had to admit that I’d never seen a bee nest in a stem either, and so I went home to do more research.
The Xerces Society, which works for insect and pollinator conservation, put together a wonderful guide to “Nesting and Overwintering Habitat for Pollinators and other Beneficial Insects.”
They explain that bees don’t nest in the growing stems, they nest in last year’s stems that are dry, hollow, and snipped off in early spring to expose an opening.
The 12-page, illustrated resource lays out a nice timeline for gardeners.
First, don’t cut down your flower stalks in the fall! Birds and other critters will eat the seeds. The structure will also help create insulating air spaces in the subnivean zone, a layer between ground and snow where many living things survive the winter.
Plus, those seed heads are picturesque when capped by snow.
Early next spring, before it warms up, is the time to prune the stalks. If you cut the stalks at a variety of heights, from 8 inches up to 24, then the resulting cavities will be different diameters, and you can support a higher diversity of bees.
Pruning shrubs at the same time can also open doors to new nest sites, because carpenter bees can excavate the soft center pith and create a tunnel.
By summer, new growth will hide those dead, brown stalks, and bees will love having nectar and pollen sources so close to home.
Solitary bees aren’t aggressive, and only sting if you accidentally squash one, so you don’t need to worry that encouraging them puts you or kids in danger.
Well, nothing. Protecting bees is easy for lazy gardeners!
If all goes well, the stems you snip off next spring will fill up with baby bees, who will also spend next winter there, and some species may not emerge until late the following summer.
The stems will naturally fall over after a few years and add to the litter on the ground – which benefits both plants and insects.
Could you just put up a bee house instead?
These bergamot seed heads were left up in the museum’s pollinator gardens and provided both blossoms of snow through the winter and bee nesting sites in the spring. Lois Nestel, the museum’s founding director, wrote, “Most people are aware of the beauty of summer flowers and often bemoan their passing as winter approaches. This need not be a cause for regret because, while much color may be lost, there continue – as seeds, pods and capsules – many forms that rival the flowers in beauty and grace.”
In recent years, both Etsy crafters and manufacturers have put many of these cute contraptions on the market. They often consist of holes drilled in wood, or a case filled with something like hollow bamboo.
The problem, according to some scientists, is that these homes aren’t cleanable. When they are left up year after year, diseases and parasites move in, and kill any bees who attempt to nest there. They can be actively harmful instead of helpful.
At the museum, our bee cabinets can be opened, and are cleaned out every couple years.
In your garden, the cut stems will naturally fall over as new stems grow, so you never have to worry about cleaning them!
With this information, native bee and flower lovers can drop those shears, step away from the garden, and go for a beautiful fall hike instead!
Emily M. Stone is Naturalist/Education Director at the Cable Natural History Museum. Her award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at cablemuseum.org/books and at your local independent bookstore, too. For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.