It may be hard to imagine finding flowers and pollinators in February, but the first flowers of the spring can already be seen blooming all across New England. Poking up from the frozen ground of swamps and stream banks, skunk cabbage (Symplocarpus foetidus) doesn’t exactly look like your average flower. It produces multiple small flowers on a central spike, or spadix, surrounded by a purplish hood known as a spathe. Few other flowers in northeastern North America share this odd floral structure – a characteristic of plants in the largely tropical Arum family, which includes popular houseplants like Spathiphyllum (peace lily), Philodendron, and Monstera.
Skunk cabbage flowering along a small stream in Massachusetts in late February. Skunk cabbage spathes are easy to overlook, but can be quite common in wetlands in late winter and early spring.
Aside from its bizarre appearance, skunk cabbage stands out from other native New England plants with another unique feature: its flowers have the ability to produce significant amounts of heat! Fueled by energy stored in the plant’s modified underground stem (called a rhizome), skunk cabbage can maintain temperatures of over 50 degrees within the spathe even as external air temperatures drop below freezing. Skunk cabbage flowers produce varying amounts of heat depending on environmental conditions as well as their age. Like some other related plants in the Arum family, skunk cabbage flowers are all female when the spathe first opens. These later become pollen-producing male flowers, with flowers at the top of the spadix transitioning first. Heat production peaks during the female phase, declining as the flowers age and begin to produce pollen.
Skunk cabbage spathe. This structure surrounds the plant’s central flower spike. Its mottled purple color may function to attract carrion-feeding flies that could act as pollinators.
Why does skunk cabbage produce heat? Despite several studies of this phenomenon, the answer is unclear. Production of heat may be necessary to allow skunk cabbage to grow and flower in a rather inhospitable environment, preventing the buildup of snow and ice around the spathe. By flowering well before most other plants, skunk cabbage may be able to take advantage of any insects that are active at this time of year, with heating performing the additional function of attracting insect pollinators. The purplish color of skunk cabbage spathes, in addition to their unpleasant smell, suggests that they may be pollinated by flies. Other primarily fly-pollinated plants share similar traits, tricking flies into visiting their flowers when searching for sites to lay eggs. By heating its spathes, skunk cabbage could provide an extra incentive for these early-season insects to visit its flowers.
Although scavenging flies hardly seem like likely pollinators, they can be quite important to the pollination success of some groups of plants that specialize in attracting them.
While flies have been documented at skunk cabbage flowers, frequency of successful pollination events seems to be quite low. Interestingly, some of the insects most often seen at skunk cabbage flowers are honey bees, which visit male skunk cabbage flowers as an early-spring source of pollen. However, it’s unlikely that honey bees act as effective pollinators, since they tend not to visit skunk cabbage’s nectarless female flowers and may not even make contact with the spadix itself, instead collecting pollen that has fallen to the base of the spathe.
Skunk cabbage provides an excellent example of just how much remains unknown about the ecology of some of our most ubiquitous (and fascinating!) native plant species. As you walk through the woods in late winter and early spring, keep an eye out for this strange plant in any area with wet soil and appreciate the incredible adaptations skunk cabbage has evolved that allow it to thrive at a time when few other flowers dare to bloom.
Early last spring, TPI was officially funded by the Tufts Green Fund. Since last year, we planted three pollinator gardens on the Medford/Somerville campus, and generated outreach materials for events on and off campus. Through live-facing events alone, TPI reached over 1,000 people in Massachusetts and Rhode Island!
For this cycle of the Green Fund, the Sustainability Committee from the School of the Museum of Fine Arts (SMFA) at Tufts University reached out about applying to fund pollinator gardens on their campus. As of yesterday, the SMFA pollinator garden project was funded!
We extend our congratulations and are excited to collaborate! Some of the seedlings we’re growing in the greenhouse, as well as TPI signs, will find a home in Boston later this year. If you see a pollinator garden while strolling the SMFA campus, take a moment to watch. You might be surprised by how many pollinators you see!
To kick off 2020, several TPI members spent two weeks in Costa Rica on a tropical field ecology trip. While there, we saw a smattering of animals and plants, such as Costa Rica’s largest weevil, kinkajous sipping nectar from balsa flowers, and scarlet macaws; we harvested coffee on a farm in Santa María de Dota and learned to identify flavors associated with high quality beans; and released baby sea turtles into the ocean. All in all, an unforgettable trip.
Of course, we also got up close with diverse pollinators. This post, written collaboratively by TPI members, highlights our favorite pollinator groups that we saw.
Butterflies: Costa Rica is home to over 1,200 butterfly species of diverse colors and sizes. The blue morpho, known for its iridescent blue, has a wingspan of up to 8 inches! In contrast, skippers often have a wingspan no larger than 1 inch. Although they look very different, blue morphos and skippers are both fast fliers and difficult to catch (in net and on camera). Here, I snapped a picture of a skipper taking a drink from…a sweaty sock!
Skipper foraging for salts on a sweaty sock. PC: Rachael Bonoan.
Although this may sound gross to us, sweat and mud puddles are an important source of sodium for skippers and other butterflies. Most butterflies only eat nectar, which provides plenty of sugar energy for flying, but is lacking in sodium. Among other things, sodium is important for water-regulation and mating in butterflies. I also had the opportunity to watch swallowtail caterpillars transition to adult butterflies. This caterpillar is in the “pre-pupal” stage—it’s beginning to shed its skin and spin its chrysalis. Once the caterpillar has spun its chrysalis, it is in the “pupal” stage. During this stage, the caterpillar undergoes many changes in order to become a beautiful butterfly!
Bats: Costa Rica is home to 112 of the over 1100 species of bats worldwide, giving the country one of the most diverse bat populations in the world, and making it an important site for bat conservation. Many native plants and crops in Costa Rica, including bananas, depend entirely on bats for pollination or seed dispersion. Bats spend their days sleeping in hollow trees and under palm leaves, and at night take to the sky in search of bugs, fruit, and nectar for food. Bats eat a huge number of mosquitos and can provide better pest control than birds in agricultural fields. They spread pollen when feeding on nectar and disperse seeds after eating fruits. And bats are the only mammal that can fly! Costa Rica is home to three species of vampire bats, and to several rare species like the honduran white bat. The next time you enjoy a banana, peach, or margarita (bats pollinate agave!) thank a bat!
Stingless bees: Although bumble bees (Bombus) are the dominant wild social bees in temperate areas, stingless bees (Meliponini) have full reign over the tropics. Throughout the neotropics, including Costa Rica, stingless bees are important crop pollinators and they are prized for their delicious and medicinal honey by bee keepers, who are known as meliponiculturalists.
Intriguingly, in addition to flowers, stingless bees also visit many non-floral resources for salt, including rotting fruit, muddy water, human sweat, urine, and even carrion. It is this last resource that sufficiently piqued the interest of two TPI members to study the foraging preferences of stingless bees on rotting meat. We hung up chicken baits that we had marinated in a variety of salt solutions and watched them over two days to determine if stingless bees are indeed going for salts when they visit meat or are instead looking for protein. Although most bees use pollen for protein, three species have switched over to a carrion-only diet, so this hypothesis is not unreasonable. What did we find? That six different species of stingless bees foraged on our baits and that they *do* have preferences: for un-soaked chicken and sodium but not for magnesium, potassium, or calcium. So, they likely visit meat for both salts and supplemental protein, and this was confirmed in our observations of Trigonafuscipennis workers flying off with pollen baskets full of meat!
Stingless bees foraging for minerals on a sodium-soaked carrion bait. Like honey bees, stingless bees recruit workers to resources, so it’s likely that all of these bees are from one colony.
Orchid bees: If you wander the forests of Costa Rica long enough, you’ll likely see a metallic green flash, darting between the trees in search of flowers. These are orchid bees of the genus Euglossa, which are among the most dramatically colored bees in the world, coming in iridescent colors ranging from bright red to blue and even violet.
Orchid bees encompass over 200
species (many of them less colorful) and constitute the most important and
abundant pollinator group in much of the New World tropics. The bees are known
to fly up to 40-km in a day, an astounding distance that helps tropical plants
mate while far apart. They also include some of the longest-tongued bees in the
world, like the gorgeous specimen of Euglossa asarophora pictured below.
That long thin line extending beyond its body is its tongue, which is long even
for an orchid bee! You can see how this might come in handy for reaching in
very deep flowers for sugary nectar.
Euglossa asarophora has an incredibly long tongue. Unlike most other bees, orchid bees suck rather than sip nectar, a behavior that prevents them from feeding on highly concentrated (and therefore viscous) nectar. PC: Atticus Murphy and Leslie Spencer.
But orchid bees are perhaps most
famous for their intricate relationships with orchids, and their highly unusual
scent collection behaviors. In an effort to attract a mate, male orchid bees
spend much of their day roaming the forest in search of specific scents, often
those produced by rare orchids. When they come across a desirable smell, the
bees scoop the smell into a specialized organ on their hind legs, where it is
stored. Some orchids have evolved to produce no rewards other than the
particular scent that their specialist orchid bee pollinator likes best! This
trait comes in handy for humans, too: by putting out synthetic perfume
compounds, scientists can attract the male bees in order to study them (or take
pictures like the one of the green Euglossa above).
Hummingbirds: Hummingbirds’ extravagant plumage and fascinating behaviors make them some of the most well-known non-insect pollinators. While only one or two hummingbird species can be found regularly in the United States east of the Mississippi River, Costa Rica hosts an astounding 50 species, ranging from the widespread Rufous-tailed Hummingbird that can be found visiting flowers on city rooftops to highlands specialties like the aptly-named mountain-gems. Like many other groups of pollinators, hummingbirds include both generalists and specialists. Some species, known as hermits, have strongly decurved bills that are well-suited for accessing the nectar of curved Heliconia flowers. Unlike many other hummingbirds, hermits are not territorial. Rather than defend flower patches, they instead visit plants scattered around the forest floor along fixed routes, a behavior known as traplining (also seen in other pollinators, such as orchid bees!). As they forage, hermits provide a valuable service for Heliconia by carrying their pollen over long distances, often to other individuals of the same species – a difficult feat to achieve for a plant growing at low densities in the understory of a tropical forest!
Rufous-tailed hummingbirds are common throughout the lowlands of Costa Rica. They aggressively defend patches of flowers from intruding hummingbirds. PC: Nick Dorian.
Although our trip taught us a lot, it also raised a lot of questions. For example, we don’t know what most orchid bees nests look like, what sorts of microbes help stingless bees digest meat-based protein, and what will happen to mountain-gems as the tops of mountains warm. We’ll just have to wait until next time to go back to the tropics to do the science and find out!
