The Feathered Bees’ Spring Arrival

RTHU in flight. PC: Michael Janke.

The smell of spring permeates the air as the grass begins to poke through the sodden dirt and buds emerge from the tips of the trees.  Concurrent with the change of seasons is another great event – hummingbird spring migration!  While there are more than 330 different species of hummingbirds (Trochilidae), only around 12 to 15 species routinely nest in the U.S.  For us resident Bay Staters’ we can expect to see even less!  The Ruby-Throated Hummingbird (Archilochus colubris; RTHU) is the only breeding hummingbird in eastern North America.

Twice a year, these tiny powerhouses undergo an 805 km migratory route—some individuals coming from as far away as the Pacific slope of Costa Rica and flying up into Central Alberta, Canada.  Despite their small size (females averaging 3.5 grams and males averaging 3.0 grams), most fly nonstop across the Gulf of Mexico during spring migration.  In Massachusetts, you can expect to see these sparkling gems beginning in mid-April.  In fact, the first sighting was just reported on eBird—an online database of real-time bird observations—in East Falmouth, MA on April 27th.

Before embarking on their migratory routes, RTHU will gain about 25-40% of their body weight, fattening up on nectar and insect.  Once they have arrived in North America, RTHU get right to work replenishing their depleted reserves.  While hummingbirds are birds, they feed similarly to insects and have appropriately been dubbed “feathered bees” by the National Audubon Society.  Like insect pollinators, hummingbirds fly from flower to flower in search for nectar.  As a hummingbird dips its bill into flowers, pollen grains stick to their feathers and bill which get carried and distributed to the next flower.  It is estimated that nearly 8,000 plant species throughout the Americas rely on hummingbirds as their primary pollinator.

Female RTHU resting on flower. PC: Nick Dorian.

Hummingbirds and plants represent a classic example of a plant-pollinator relationship and demonstrate coevolution—the phenomena of intimately linked organisms influencing each other’s evolution.  Hummingbird-dependent plants have evolved several “pro-bird” traits including sucrose-rich nectar, brightly colored, unscented flowers (smell is important for insects to find flowers, while birds rely on vision), and tubular flowers that allow easy access for hummingbirds.  Like other pollinators, when native plants thrive, so do hummingbirds.  To sustain a heightened metabolism (their hearts beat as fast as 1,260 beats per minute after all), hummingbirds eat once every 10 – 15 minutes and visit between 1,000– 2,000 flowers per day!

Unfortunately, the preferred habitats of RTHU are changing along their migratory routes due to habitat conversion and climate change.  There has been an increase in the concern about the conservation of pollinators in urban environments.  A known way to mitigate the impact of urbanization is through native plants gardens which provide both habitat and resources for pollinators.  Such efforts can also encompass native plants with specialized hummingbird-pollinated flowers in urban landscaping.  In the northeast, planting red cardinal flower (Lobelia cardinalis) or trumpet honeysuckle (Lonicera sempervirens) in your garden may contribute to community restoration and ecosystem functioning by attracting RTHU—and who wouldn’t want these cuties flying around their yard?

Female RTHU drinking from L. cardinalis. PC: Max McCarthy.

Do you want to start your own pollinator garden this year, but don’t know what plants to get? Come to our Grab-n-Grow Native Plant sale next month to stock up on all thing native plants!  More information can be found at: https://sites.tufts.edu/pollinators/cultivate/native-plant-sale/.

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.

To learn more, check out this useful guide produced by University of Minnesota Extension.

From where do the springtime butterflies come?

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?

Well, the answer depends on which of New England’s 100+ species of butterflies we consider!

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.

Great Spangled Fritillary. PC: Nick Dorian

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.

Eastern Tiger Swallowtail. PC: Nick Dorian

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.

Mourning Cloak. PC: Max McCarthy

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 mate.

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!