How To Support Overwintering Native Bees. Want To Support Biodiversity in Your Garden? Leave Sites for Native Bees To Overwinter
- Oanh Nguyễn
- May 3
- 4 min read
by Kate Wilson
Originally published in the 2022 December Issue of the WildFlower News
Co-evolution of flowers and bees
When people are exploring the diversity of our aspen parkland’s wildflowers, they may also be learning to appreciate the remarkable variety of its native bees. This is why a recent finding by an international expert in paleobiology is compelling news,
shedding new light on when the diversification of both became intimately linked.
And it goes back a long way.
In late 2020, professor George Poinar Jr. of Oregon State University identified a fossilized female bee in amber from 100 million years ago. While this pushed back the fossil record for bees’ first appearance, the significant finding was the numerous pollen grains present. Also clinging to her body were beetle parasites – the kind that hitch a ride to bees’ nests to dine on their larvae and food left by the bee. Both indicated she had visited one or more flowers.
Because Poinar’s primitive bee shared traits with both modern bees and apoid wasps – which are carnivorous – his finding more accurately pinned the time when bees split off from wasps and became pollen eaters. While science is still working on why bees made the transition to flowers, from that point on bees became the standard-bearers for driving the diversification of flowering plants.
The earliest animal-pollinated flowers were shallow and cup shaped, visited by insects such as beetles. As bees became specialized as pollination agents – with behavioural and physical modifications such as scopal hairs and pollen baskets – flowers developed rewards such as nectar and longer tubes, which offered advantages for bees with longer tongues.
It meant that flowers with the most attractive scents and colours had advantages over other flowers, as they enticed greater numbers of pollinating bees and butterflies. Researchers in southern England have even found that bee body weight and the rate they visit flowers influences what flowers they select.
This interdependent relationship stimulated what is known as adaptive radiation of the angiosperms, and in turn, the bees themselves. Diversification of both went into high gear. It also highlights an essential partnership. Native flowers in Alberta’s aspen parkland are dependent on pollination by the roughly 130 species of bees that share the landscape – as well as other pollinators – and bees rely on a variety of both native and agricultural plants.
After expanding dramatically in the warming trend that followed the end of the last Ice Age, about 11,700 years ago, the variety of bee species we see today are well adapted to the aspen parkland’s native plants. While most are generalist, some are specialists, gathering pollen from one or a few species or genera of closely related plants. A select group of bee specialists even gather floral oils. And agricultural research is starting to show how wild bees can provide the majority of crop visitation, while bee species richness can increase fruit set of orchard crops.
Slightly untidy gardens are best for overwintering bees
When it comes to helping native bees survive the winter, it’s useful to be familiar with some of their needs and habits. Almost all of Alberta’s bees lead a solitary life, and most survive the winter as larvae. The adult female, after laying her eggs in a burrow or other cavity, will not live to see her young emerge in the spring and summer. But there are exceptions.
Late in the summer, bumble bees, for instance, will die except for the new queen. After mating, she will find a hibernation spot and emerge in the spring to build a new nest to raise her young. Many halictid bees, known as sweat bees due to their attraction to people’s sweat, overwinter as mated adult females, emerging in the early spring.
In order to secure winter protection, many species seek out cavities provided by material such as loose bark or dead leaves. For bumble bees, a perfect spot is an abandoned rodent nest or within a piece of wood or compost pile. Other bees overwinter underground.
Andrenid bees, for instance, hibernate in underground tunnels and emerge in the spring before most plants get started. If you’ve noticed these little yellow and black bees in your garden, there’s a chance they are also overwintering. Where there’s a patch of bare soil, maybe on a dirt path or south facing incline, it could be a location for ground nesting bees.
Whatever their life cycle, all bees need sheltered places to survive the winter either as pre-pupae or hibernating adults. So if you choose to tidy up debris or dig up spots of packed bare ground, be aware that you may be removing next season’s generation of bee pollinators. Tilling the soil can destroy ground nesting bees’ burrows, and clearing away too much dead material in the fall removes critical shelter from winter elements.
Slightly ‘untidy’ gardens are one of your best practices for supporting overwintering pollinators. Refrain from pulling out dead plant material, especially around hedge and shrub bases, and consider allowing a patch of your lawn to grow longer before winter sets in.
If you want to deadhead the more profuse garden plants, make sure to leave a section of stalk on those with hollow or pithy stems such as giant hyssop, raspberry and sunflowers (see photos above). The hollow stalks provide great hibernation sites, and removing them in the fall could be fatal for any bees that are nesting in them. The Canadian Wildlife Federation suggests burying logs halfway and leaving tree stumps.
If you don’t want your garden too wild looking – to alleviate unhappy neighbours or even bylaw infractions – try arranging piles of branches artfully in or around your garden space for the winter.
One final consideration: the timing of bees’ emergence after wintering influences which flowers are important to them. Early- emerging species, for instance many Andrenid bees, rely on early-blooming flowers such as willow and dandelion. So leaving spring ‘weedy’ flowers un-mowed is a good practice for giving those early emergers an edge as they come out of hibernation.
To see the article on the fossilized primitive bee, go to www.sciencedaily.com/bees-selection-flowers.
To find out more about supporting native bees:
