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.
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.
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.
You likely learned in grade school, from Heimlich in a Bug’s Life, or from the Very Hungry Caterpillar, that every butterfly undergoes metamorphosis. For all butterflies, this phenomenon involves four distinct stages of development. An individual starts as an egg, breaks out as a caterpillar (or larva), eats leaves until it’s ready to pupate into a chrysalis, and subsequently emerges as an adult butterfly. Adults fly around to mate, feed on flower nectar, and produce the next generation. A successful butterfly not only has to make the transition from egg to larva, pupa, and eventually adult, but in New England, also has to endure six months of cold, harsh conditions. So how do such delicate creatures make it through the winter?
Some butterflies spend the winter as small, immobile, and defenseless eggs. Once such species is the bog copper Lycaena epixanthe which thrives in undisturbed cranberry bogs of New England such as those found on Cape Cod. Adults lay eggs on the bottom of cranberry leaves near the surface of the bog. These eggs are built to withstand not only winter freezes and thaws, but also periodic flooding. Caterpillars break out of their eggs in the spring and begin chowing down on cranberry leaves, their favorite food. Other gossamer-wing butterflies like Coral Hairstreak Satyrium titus and Oak Hairstreak Satyrium favonius spend the winter as eggs on their favorite trees, black cherry (Prunus serotina) and oaks (Quercus spp.), respectively. Eggs are situated safely in the crevasses of the tree bark and branches, at the roots of the tree, or in the leaf litter surrounding it.
The majority of butterflies spend the winter as caterpillars.
Typically, these species begin feeding as caterpillars before winter to amass
nutrients and fat for the long dormancy ahead. Then, when the weather cools, they
find someplace safe from the elements, often underground or in the leaf litter.
Other species like Viceroy Limenitis Archippus build their own houses
for winter, known as hibernacula, by twirling poplar or willow leaves using
silk. Not all species go about it this way though; the Great Spangled
Fritillary Speyeria cybele, spends its winter as an unfed larva so that its
life cycle is timed with the availability of violets.
Then there are species that spend the winter as a chrysalis. In this intermediary stage between caterpillar and adult, the butterfly completely reorients its body and restructures itself. The chrysalis is a very hardy life stage, which is why all swallowtail butterflies (Papilionidae) spend the winter in this form. Black swallowtails Papilio polyxenes, like many of their relatives, affix their chrysalises to a tree’s bark or branch, held in place by a thin, but strong, thread of silk. Often these dormant individuals will cryptically blend in with the branch or the leaf on which they’re placed. The Canadian tiger swallowtail Papilio canadensis, withstands the winter cold by amassing high concentrations of ethylene glycol in the chrysalis. This compound is such an effective cryoprotectant that it’s the base compound for commercially manufactured antifreeze.
Although some butterflies do overwinter as adults in New England, it’s
a rare strategy. The most readily seen of these species is the Mourning cloak Nymphalis
antiopa. The Mourning cloak is often the first butterfly seen in the year,
coming out before snow has fully melted, and even capable of coming out on
particularly warm winter days to sun. This is because it has a high concentration
of glycerol, another cryoprotectant, which makes it difficult for damaging ice
crystals to form in its body. The Eastern Comma Polygonia comma and
Question Mark Polygonia interrogationis are two other species which also
have the capacity to withstand cold New England winters. These remarkable
butterflies will find crevasses in trees, beneath bark, or under rocks and buildings
where they will be ready and waiting for the earliest signs of spring to emerge
And last, but not least, there are also butterflies that choose to avoid the bad weather entirely! There are only two species of migratory butterflies found in New England, which leave for the winter and come back for next year’s spring or summer. The Monarch Danaus plexippus butterfly heads south to the warmer climes of Mexico, where millions of butterflies will gather in massive aggregations in oak-pine forests. The Painted lady Vanessa cardui is another long-distance migrant, though its journey is less directed than that of the Monarch. In Europe, the species is known to embark on transcontinental migrations from the northern parts of Europe to the Sahara Desert. The details of its journey in the eastern United States remains to be known.
The diversity of overwintering approaches among butterflies demonstrates the capacity of small insects to adapt in hostile environments. When you see your first butterfly of the year, consider how they might have managed to make it outside while we’re spending time by the fireplace with hot cocoa. You also might think twice about cleaning up your leaves until the beginning of summer to give butterflies who overwinter there a chance to emerge! For other tips on supporting butterflies and other pollinators, check out our January blog post!
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. We, 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!
How do I know I’ve found a cellophane bee? 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 on their face.
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!
What flowers do cellophane bees like? Shrubby willows (Salix), red maples (Acer rubrum), redbud (Cercis canadensis), plum (Prunus), and apple (Malus).
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.