The right way to leave stems for native bees

About 30% of New England’s native bees build nests above ground. Besides bee hotels (many of which have their own issues), a great way to support these above-ground nesting bees is to leave dead plant stems standing in gardens. Bees will lay and provision offspring in these hollow or pithy stems. TPI members are often asked by gardeners, “when is the best time to cut down stems?” The answer is at least two years (ideally never), which is longer than you might think. Let’s review bee and plant biology to understand why.

Year 1: Plant stems are growing. Native plants like joe-pye weed, elderberry, wild bergamot, mountain mint, and swamp milkweed produce hollow or pithy (e.g. soft, spongy tissue) suitable for nesting bees. Bees won’t nest in these actively growing stems. At the end of the growing season (December through March), cut the stems back to between 6-18” tall. Use sharp tools to ensure a clean cut. By cutting back the stems, you have created homes for next year’s bees.

Joe-pye weed (Eutrochium purpureum) stems were cut back in December 2020. The stems are hollow and will provide homes for twig-nesting bees during the 2021 growing season. TPI will leave them stems standing until the end of the 2022 growing season to ensure that all bee offspring have emerged.

Year 2: Bees active during this year will nest in the stems you left standing. They will lay eggs in the stem and provision each egg with a nutritious ball of pollen and nectar. Inside the stem, bees will develop from eggs into larvae and adults that hibernate through winter. Bees won’t emerge from stems until next growing season. Remember to cut back the new, green stems produced this year for next year’s bees.

Leafcutter bees (Megachile sp.) will live in your garden if you provide undisturbed stems for them to nest in.

Year 3: In spring of year 3, stems produced in year 1 still contain bees; stems produced in year 2 do not contain bees. Leave both generations of stems standing throughout the year. Spring-active bees will emerge from year 1 stems by June, whereas fall-active species might not emerge from year 1 stems until August or early September. During this time, new bees will nest in year 2 stems, so leave them standing!

While this may seem like an awfully long time to leave stubble in a garden, it is the only way to ensure that native bees find safe, undisturbed places to nest. Posting signage in your garden to inform visitors about how gardens can be managed to balance aesthetic and ecological goals can be helpful.

Bee a community scientist: report sightings of cellophane bees!

Unequal cellophane bees (Colletes inaequalis) herald spring in the eastern US. Bees emerge on the first warm day, when snow is still on the ground. They get right to work searching for flowers to feed on after a long winter. And, as spring comes earlier and earlier, bees are coming out earlier. Pollinator scientists at Tufts University, want to learn more about how the annual schedules of bees are affected by climate change. And we need your help!

What can I do? Report any sightings of unequal cellophane bees to iNaturalist or via this form (but not both). To learn how to spot one, check out our cellophane bee field ID guide, watch our video, and read on.

How do I know I’ve found a cellophane bee? Unequal cellophane bees live east of The Rockies and from North Carolina to Ontario. They are slender and macaroni-sized, ~0.75x the size of a honey bee. They are fuzzy with bold white stripes over a black abdomen and they have “cute” heart-shaped faces. Unlike similar sized mining bees (Andrena spp.), females do not have shallow, vertical grooves (foveae) on their face.

female cellophane bee in nest entrance
Female cellophane bees sun themselves in nest entrances. Look for their “heart-shaped” faces without vertical grooves.
female cellophane bee (Colletes inaequalis) on prairie willow
Females have bold stripes on their abdomens and sand-colored hair on their thorax and face.

What do their nests look like? Cellophane bee nests look like tiny volcanoes of sand (think ant hill but with an entrance about the width of a pencil). They nest in aggregations, meaning one nest is surrounded by many others of similar size and shape. Aggregations often form in disturbed areas or sparsely vegetated ground on sunny slopes. Cemeteries, walking paths, and river banks are all good places to look!

cellophane bees nest in aggregations
Cellophane bees nest in aggregations on sparsely vegetated slopes. Look for volcanoes of sand!

What flowers do cellophane bees like? Shrubby willows (Salix), red maples (Acer rubrum), redbud (Cercis canadensis), plum (Prunus), and apple (Malus).

Females (left) are slightly bigger than males (right). Both visit flowers for nectar.

Do I have to worry about being stung? Don’t worry, cellophane bees are docile! Each female takes care of her own nest, which takes a lot of time and energy. She wouldn’t risk getting involved with a giant human.

Questions? Check out this video or send us an email.

Five easy ways to support pollinators in 2021

2020 was a rough year for everyone, including pollinators. Asian giant hornets arrived in Washington state, threatening honey bees; western Monarch butterfly numbers were the lowest in the past 30 years; neonicotinoid pesticides continue to be approved for use in the United States; and endangered rusty-patched bumble bees did not receive critical habitat because their biology is too poorly understood. That’s just the start.

Pollinators face a relentless barrage of threats from humans. The main factors driving pollinators declines include habitat loss, pesticides, climate change, light pollution, and the spread of exotic species and disease. Recently, scientists framed pollinator declines as “death by a thousand cuts,” underscoring that no single factor is solely responsible. Rather, the combination of multiple factors working in tandem is the greatest threat.

With this in mind, 2021 is a perfect year to resolve to make a small change in your lifestyle to support pollinators. Inspired by a recent list of actions to conserve insects, TPI proposes five actions you can take in 2021 to make a difference in the lives of urban pollinators:

1. Grow native plants. Native plants are beautiful and adapted to the local environment, meaning they require less water and fewer chemical inputs compared to ornamental plants. Even more, they offer food (pollen, nectar, leaves), nesting sites, and shelter for pollinators. Native plants also provide cultural benefits in the form of reconnecting community members to their local environments. Interested in growing natives? Check out our native planting guides and stay tuned for details regarding TPI’s native plant sale during 2021 national pollinator week.

Plant native goldenrod to assist eastern Monarch butterflies on their fall migration to Mexico.

2. Reduce your pesticide use. Pesticides are nasty chemicals that are widely used to suppress pest insects and weeds, but also cause non-target effects in pollinators. In spite of successful efforts in Europe to increase regulation on these pesticides, as well as ongoing campaigns here in the U.S., many harmful chemicals remain available to consumers worldwide. On average, lawns receive ten times more pesticides than do conventionally grown crops. Use pesticides judiciously and in a targeted way; avoid broad applications and claims by companies to “eradicate mosquitos.” Remember: any product that kills a mosquito also kills a bee.

3. Turn off your lights at night. Artificial light at night (ALAN) is one of most recognizable signatures of humanity from space. Yet, it also spells disaster for nocturnal pollinating insects like moths and beetles. Insects attracted to lights are easily picked off by predators and are worse at finding mates. As a result, insect populations suffer in areas with high ALAN such as cities. To curb declines of nocturnal pollinating insects, install motion-activated lights, replace bright blue-white lights with softer red-orange ones, or plant a moon garden containing night-blooming plants. Let’s keep our skies dark.

4. Shop local and support farmer’s markets. Many growers and vendors in Somerville and Medford near Tufts University (like the Somerville Winter Market and Neighborhood Produce) are committed to supporting pollinators by selling pesticide-free, locally-made products. Shop there as often as possible in order to avoid less insect-friendly alternatives at larger chain stores.

5. Educate others and share this post. Urban pollinator conservation depends on the active participation of the community. Become an advocate for pollinator conservation by writing to your politicians, installing a yard sign, or by simply talking about it—to your kids, your friends, your neighbors, your hairdressers, your bakers, your baristas. Teach them that bees come in all shapes and sizes or challenge them to notice their first monarch butterfly of the year. Simple awareness of pollinators—getting people to notice their environment—is the goal.

Have you made any pollinator resolutions for 2021? Let us know! We’d love to hear from you.