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.

Pollinator Week BINGO!

Every year, a week in June is dedicated to celebrating pollinators. All week long TPI will be posting pollinator-related videos, blog posts, etc. PLUS, you can play BINGO for a chance to win a prize!

To play Pollinator Week BINGO, which features flower-visiting insects you can find in the Northeastern USA this time of year, download and print the Bingo card (below) or screen shot the image on your phone. Take your card/phone outside and if you find the correct insect, mark it off on your printed card with a pen/pencil or with your phone’s photo annotation option.

If you get BINGO! (five in a row, vertical, horizontal, or diagonal, TPI logo is a free space), send a photo of your annotated card to tuftspollinators@gmail.com or tweet a photo and tag @PollinateTufts by 11:59 pm on Friday, June 26. Each completed BINGO! card will be entered in a drawing to win TPI swag and a voucher for a free pollinator-friendly plant at next spring’s TPI plant sale! Limit one entry per person.

For help identifying the insects you observe, download our identification guides or reach out to us with photos via email or Twitter!


Stay tuned for more #PollinatorWeek fun!

Social distancing with cellophane bees

Cellophane bees are very bad at social distancing. In early spring, hundreds to thousands of males and females aggregate on sandy soil and in pines and cedar trees. Males swarm females in large groups termed “mating balls” and, from each cluster, only one male will emerge victorious. Once mated, females get to business building nests. Though solitary, females work in a shared office space called a nesting aggregation for their three-week life. Sometimes, when a female gets bored, she’ll even dip into the nest of another female. Certainly, they do not keep six feet away from each other in the narrow tunnel of the nest. Don’t be like cellophane bees. Practice social distancing.

Cellophane bees are very bad at social distancing. Here, several males have swarmed a female and are competing for the chance to mate with her. PC: Colletes succinctus, Nigel Jones, Flickr

Nevertheless, observing cellophane bees is a great way to social distance while you’re at home and living your best #quarantinelife. In New England, you can find unequal cellophane bees (Colletes inaequalis) nesting in your backyard in late-March/early-April, provided the sod isn’t too thick. Watching cellophane bees be cellophane bees can be a fun distraction. And don’t worry about getting stung since they are quite docile. Here’s a short video to help you get started finding your own cellophane bee nests. If you do find some, take a photo and get in touch! We’d love to hear what you find.

Female cellophane bees nest in close proximity. Each turret of sand marks the entrance to a nest. PC: N. Dorian