You need a bit of patience to see a Small Carpenter Bee, genus Ceratina, well. I caught this little male, put him in a jar in the freezer, and then took photos as he woke up (yes, this is all quite rude). I let him go right where I found him and will forever cherish these little bees when I catch them zipping around our flowers. (Image: Brendan McGarry)
Recently, I was out in my garden pulling up old pieces of bamboo used for fencing around some fragile native plants getting established. I was in the process of making a pile of them to burn, when I noticed several had their hollow ends delicately cemented in. Several years ago I would have thought almost nothing of this, but these little plugs brought me back to spring and the delights of plants and their pollinators. It was a gentle reminder that life is still going, even in the middle of winter.
Until I started learning about bees through the Washington Native Bee Society, joining the Washington Bee Atlas, and studying to become an Apprentice Master Melitologist through Oregon State University (half measures be damned), I probably wouldn’t have had much to say about what bees are doing during the winter. Or rather, I probably wouldn’t have even realized it was a question to ask. Most of us know that insects aren’t out in force during the winter and we generally understand they have to go somewhere during that period of time. But most of us don’t dwell on these ideas and certainly don’t consider them when we go about our annual gardening tasks.
The capped off ends of my bamboo poles were almost certainly created by a Mason Bee. These members of the genus Osmia are well known for their pollination services (they are much more efficient pollinators than European Honeybees), as well as their particular style of nest.
Finding a suitable hollow, be it a bamboo stick, a beetle hole in a log, or a cavity in the side of your concrete foundation, a female mason bee spends most of her adult life filling these spaces with chamber after chamber for her young. Various species use clay, gravel, soil, and even masticated plant material to brick in individual nest chambers for each egg, carefully provisioned with enough pollen and nectar to carry the occupant through to the point of emerging as an adult bee. And then, after a hopefully long, uneventful life of mating, masonry, egg laying, and pollen and nectar gathering – the female mason bee dies and leaves those provisioned young to figure it out.
A Mason Bee using a human provided nesting block. The caps on these holes match those of the bamboo in my yard. (Image: Brendan McGarry)
Right now, there are bees laying in wait for spring and summer all over the Hill. There are probably ones in your home’s exterior walls, in the compact ground, in the plants that still haven’t pruned back.
A vast majority of those bees are univoltine, meaning they only produce one brood of young per year (or season). How they handle the time between egg laying and emerging as adults (remember, insect development is generally egg, larvae, pupa, adult) is as varied as their nesting structures and other life history specifics. But, a majority go through what’s called pre-pupal diapause. Once a female bee leaves her eggs with provisions, they are on their own to hatch into larvae and eat through their stores. Then, once they are just about ready to pupate, they stop doing anything and sit for upwards of nine months. The following spring (or summer depending on the species) the larvae once again become active, pupate, and emerge as adult bees. Rinse and repeat.
Pikes/Pines has regularly featured bees over the past decade, so for many it won’t be a surprise that the vast majority of our native bees almost never sting, are better pollinators than honey bees, and don’t create hives or stores of honey for a colony (bumble bees are the exception). They also mostly go unnoticed because many are tiny and few let you observe them closely, even in flowers. And because they don’t live their lives in even a vaguely similar way to honey bees, their conservation looks very different. In our yards and greenspaces we can take a suite of actions that support native bees through their winter siestas and most aren’t very drastic; mostly it just means leaving well enough alone or altering some garden management habits.
Many of our most common native bees nest right in the ground. Their nests are easy to miss, consisting of only a tiny pile of soil near the entrance hole and a single female bee provisioning her future brood. The curse of the soils on the Hill is that they are a jumble of churned up glacial outwash, clay, and a hundred years of human refuse – not the best substrate for a flourishing garden. Understandably those of us lucky enough to tend a bed or two of plants amend with compost or mulch to keep weeds down. These practices are broadly championed as important aspects of improving soil fertility, but they also run afoul of native bees (not to mention a host of invertebrates, fungi, bacteria, and more) who lay their eggs in the soil. That next brood of bees can become entombed, unable to dig out through the newly applied layers.
While not truly social like Honey Bees (which live in a cooperative hive), some ground nesting bees do create aggregations of separate nests. These nests that I found on San Juan Island were probably from bees in the genus Anthophora, the digger bees. Fast flying, hairy, and about the size of a bumblebee, Pacific Digger Bees, Anthophora pacifica, are a likely spring bee to see on the Hill. (Image: Brendan McGarry)
My solution to this conundrum is to mulch less heavily than I used to (an inch at most), and skip a few garden beds each winter, particularly if I notice a lot of bee activity in a specific area. Plus, a lot of the native plants I have started spreading about don’t need as heavy handed an approach to soil treatment because many are used to our native soil conditions. I also make sure I leave some areas with bare soil or gravel entirely alone. The patches of soil around rock steps in our yard always have little bees in the genus Andrena, the mining bees, nesting in them.
Mason Bees, and many of their relatives like to use any available cavity of the right diameter and depth for their nests. If you pay enough attention this coming spring, you might notice a darkly metallic bee visiting holes in house siding or other outdoor buildings. If this female bee finds the right place to start a brood you’ll eventually find it capped off with a lid, just like the one I found in my bamboo fence. The good news is that these bees essentially never excavate, they just use whatever they can find (a notable species not in our region uses snail shells) and are entirely harmless to your structures. If you find them and can’t handle the idea of sharing space in the long term, at least give the occupants a chance to emerge in the spring and fill in the holes once they’ve been vacated.
These two bundles of leaves are individual nest cells of a Megachile bee, a Leaf Cutter bee related to mason bees. Unfortunately I found them after digging into a pile of compost. I did my best to replace them but they probably didn’t make it. This kind of disturbance is very common in our managed landscapes but in some cases it can be avoided. (Image: Brendan McGarry)
Plenty of people get excited about “bug” or “bee” motels, some variously constructed bundle of holes waiting for use by invertebrates for overwintering or nesting. At face value they seem excellent things to add to our yards, and Mason Bees will readily use them. However, all too often these become hosts to nest parasites that plague bees or simply congregate bee predators to one place.
Insects can find their own spaces just fine if we don’t spend all our waking hours trying to scrub and perfect our landscaping. Most Mason Bee keepers take a very active role in the bee lifecycle to boost fruit production. Unless that’s your goal, or you are willing to put in time keeping a “bee hotel” clean and ready to use each year, it’s probably better to just let the bees naturally disperse in your landscape and be tolerant of them using your buildings’ little cracks to rear their young every once in awhile.
Inside your prize rose stems, those dead elderberry branches, and the canes of blackberries you neglected for a few years, there are likely bees waiting out winter. Several common species of bees, the Small Carpenter Bees in the genus Ceratina, and Masked Bees in the Genus Hylaeus make good use of the pithy center of a wide variety of plants native, introduced, and ornamental. They and other species also use the hollow stems of last year’s flowers.
A Masked Bee, genus Hylaeus using an exposed cut on a rose to access the easily accessible pithy center. This bit was already dying back and it really poses no threat to the rose. In a more wild setting these bees would also benefit a plant they nest in by pollinating them. (Image: Brendan McGarry)
If you are a garden cleaner but want to help native bees, you may want to think twice about your methods, or consider avoiding raking, cutting back, etc. entirely (in a lot of cases it’s not really all that necessary from a plant health or ecological perspective). I like to leave my flowers’ seed heads intact through the winter (also a nice way to feed birds without needing feeders), and deadhead, leaving the old stems in place, in spring. This gives newly emerging flower stems room to grow, new hollows for bees, and lets last year’s bees emerge without bother. And if you can handle not over managing your garden, it saves you time for more important things like growing native plants (yes, I am biased).
Just letting your plants and greenspaces do their thing is one of the best actions we can do to support overwintering bees and other invertebrates. I know it’s hard in practice and I am not suggesting everyone should let things go entirely. But leaves left in place are truly wintering places for a wide variety of species and usually are a beneficial mulch for the plants that lost the leaves in the first place. Keeping your spade out of the ground and minimizing your snipping and shearing will let insects thrive – this is one of the next steps in ecological gardening after ceasing the use of pesticides, over fertilizing, and fetishizing the lawn. And certainly a few “pest” species may come with this approach, but I’ve often found that if I give space for lots of species, many issues sort themselves out without my active involvement.
You might have read through this and wondered “ but why should I care about native bees?” If that is truly a question you are asking, you might have felt your pulse quicken when I mentioned how good Mason Bees are at pollinating. But I find the motivation to protect nature that is rooted only in knowing what services said natural things provide people is shallow at best. It’s like appreciating a car that works great, but hating it when it’s no longer functional (even if you were the reason it doesn’t start). My real answer is that bees are extremely cool, beautiful, and easy to share spaces with. They complement our greenspaces, live complex lives, and deserve our respect as fellow species on the Hill throughout the year.
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