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The annual April battle between winter and spring in Vermont. Mount Ascutney, Vermont © Kent McFarland

Field Guide to April 2021

Migrating birds, blooming flowers, and (of course) mud season. April in Vermont is upon us, and spring is here!

By Vermont Center for Ecostudies April 1, 2021
Pair of West Virginia White butterflies creating the next generation. © Kent McFarland
Pair of West Virginia White butterflies creating the next generation. © Kent McFarland

A Spring Ephemeral Butterfly: The West Virginia White

Help Us Record Their Phenology and Range

By Kent McFarland

It’s not a gaudy butterfly. It isn’t the biggest or the smallest. In fact, it’s mostly just white. But this butterfly is unusual; it only flies in forests. Its an ephemeral spring wildflower groupie.

To see this butterfly you need to get to rich, mature hardwoods with spring wildflowers early in the season. Our other, more common veined white, the Mustard White, does fly in woods, but it has distinct dark veins in its first brood (when it may be confused with West Virginia White). The West Virginia White always has faint gray scaling along the veins. And, unlike the Mustard White, it only flies early in the season. Their flight is slow and close to the ground. Follow a woodland stream until you find the host plant–and the butterfly. Its caterpillars only feed on Crinkleroot (Cardamine diphylla) and Cut-leaved Toothwort (Cardamine concatenata).

But there’s a dirty player in the field: introduced Garlic Mustard (Alliaria petiolata). Garlic mustard was first found in the United States about 1868 on Long Island. Invasions of Garlic Mustard are causing local extirpations of toothwort, and chemicals in Garlic Mustard appear to be toxic to West Virginia Whites–yet the adults are attracted to it and lay eggs on it.

10007, , Two-leaved Toothwort Cardamine diphylla, , , image/jpeg,, 1666, 2500, Array, Array © Kent McFarland
Two-leaved Toothwort or Crinkleroot (Cardamine diphylla) © Kent McFarland
11163, , Garlic-Mustard-Alliaria-petiolata_KPMcFarland-2_580x800_acf_cropped, , , image/jpeg,, 580, 800, Array, Array © Kent McFarland
Garlic Mustard (Alliaria petiolata) © Kent McFarland

Adult West Virginia White butterflies only fly in spring before trees are fully leafed out. They are largely finished for the year by the second week of June. Extreme dates in Vermont are 12 April 2006 in Bennington (T. Armada) and 5 June 2003 in Sandgate (D. Rolnick).

Learn more about the West Virginia White at the Vermont Butterfly Atlas.

Help Us Monitor Populations, Phenology and Range in Vermont and Beyond

Spring is changing. The snow is melting earlier, wildflowers are blooming sooner, and trees are leafing out faster. How are West Virginia White butterflies faring? Help us monitor them. Find a patch of rich, hardwood forest and start walking a transect counting all the butterflies you find and reporting them to eButterfly. Even if you don’t find any butterflies, zeros are important to report too! Can you break the early or late record for a West Virginia White sighting? Who will have the highest count? Can we find them in places they’ve never been recorded? We can’t wait to find out!

11117, , hepatica, , , image/jpeg,, 750, 563, Array, Array © Julia Pupko
Sharp-lobed Hepatica © Julia Pupko
11118, , hepaticaflower, , , image/jpeg,, 720, 960, Array, Array © Kent McFarland
Sharp-lobed Hepatica Flowers © Kent McFarland

Happy Hepatica

By Julia Pupko

Strolling through the woods of Mount Ascutney, Vermont, I breathed a sigh of relief. Spring is here! The air was warm, and for the first time in months, I could see bare patches of ground with snow-melt sodden soil, leaf litter, and the occasional withered herbaceous plant. As I continued wandering up the mountainside, I paused to hoot back at a Barred Owl. Mid-hoot, I noticed a flash of green. “Who is this?” I thought to myself. Bending over, I found none other than a Sharp-lobed Hepatica (Hepatica acutiloba), with its happy red and green leaves soaking up the sunlight.

In Vermont, we have two species of Hepatica—Sharp-lobed Hepatica and Round-lobed Hepatica (Hepatica americana). These species were once lumped together, considered to be subspecies, but are now widely considered to be separate species. Hepaticas are evergreens, meaning that their leaves are retained over the course of the winter. Therefore, when the snow melts, their leaves are exposed and ready to begin photosynthesizing. This is beneficial, as both of these species are spring ephemerals, meaning that they quickly produce flowers in early spring before the trees have leafed out and blocked much of the sunlight from the forest floor.

Hepaticas have fibrous roots, with several three-lobed basal leaves emerging from the roots. In early spring, Hepaticas are some of the first species to flower; Sharp-lobed Hepatica has been recorded to flower earlier than Round-lobed Hepatica. Both species produce several lilac, pink, or white flowers, each on its own hairy stalk, which emerges from the roots. While the flowers emerge and open their petals, the leaves that remained over winter begin to wither and die. Both species are thought to be pollinated through a combination of self-pollination and insect visits, and both species are important food for some of the early-emerging bees and other pollinators. As the flowers mature into their fruiting-body achenes, new basal leaves begin to emerge.

An interesting adaptation of the Hepaticas is that their achenes attract ants, which help to disperse the seeds. Seeds will germinate over the course of the summer and winter, requiring a warm and cold period, sprouting the following spring. Keep your eye out for these marvelous little plants as you enjoy the forest this April!

A cluster fly (genus Pollenia) © Spencer Hardy
A cluster fly (genus Pollenia) © Spencer Hardy

What’s Eating Pete: Farmhouse Cluster Flies

By  Pete Kerby-Miller

Bzzz… Tap! Bzzz…. Tap! Bzzz… Tap! I’m enjoying spring sunshine in the home office these days, but the irksome buzzing of cluster flies on the window is not something I missed. While the flies’ persistent failed escapes are a merely minor annoyance to me, for the earthworms in the garden out the window that noise (had they ears to hear it) would instill fear in each of their five hearts. Those flies are quite literally cold-blooded worm killers.

The adult cluster flies (Pollenia rudis, I think) at my window have weathered the worst of winter in the walls and attic of this farmhouse. With spring temperatures, they become more active and females seek moist areas with plenty of surface vegetation–a sodden lawn will do–to lay their eggs. This is ideal habitat for the earthworm hosts of larval flies. When those eggs hatch a few days later, the maggot-like larvae crawl below ground in search of hosts. These larvae can’t burrow themselves, instead they are reliant on existing holes in the soil. Interestingly, some worm species block the entrances to their tunnels with piles of castings, effectively barring Pollenia larvae from entry. However, roots also form soil openings that these larvae can use to venture below ground. If the larvae don’t come across a worm within three days, they die. If they do find a worm, they’ll chew through its outer skin then feed off the worm from the inside out until it is either entirely consumed or so rotten they have to find another worm.

After feeding on several worms and molting three times, cluster flies will emerge as their familiar adult form. The adult flies tend to engage in “hill-topping,” a common insect mating behavior where males gather at high local elevations and compete to remain at the most desirable site at the top. This game of king of the hill can be considered a form of lekking, the behavior more often associated with birds that congregate for fantastic displays of male-male mating competition. For cluster flies though, hill-topping is just as likely to occur on top of a roof as on top of a ridge. The tendency for those flies to gather on top of buildings to mate could be linked to them finding their ways into farmhouse attics.

Both the common cluster fly and its earthworm host are introduced species originating in Europe. The flies have not only become established in North America, but seemed to have undergone some fascinating natural history adaptations. In Europe, cluster flies have annual life cycles, with larvae remaining in the soil for nearly a year and overwintering in a dormant state. In North America, eggs hatch, larvae molt, and adults emerge all within 45 days. The flies at my window today have overwintered as dormant adults in the walls. Their offspring and the following generation will complete their life cycles in under 50 days, with a fourth overwintering generation being produced in the fall. We don’t really understand what causes this drastically different life cycle between populations of this species on each side of the Atlantic. There’s still much to learn, so for now I’m hanging up the fly swatter and taking a moment to appreciate the farmhouse cluster flies.

A fully open willow flower. © Spencer Hardy
A fully open willow flower. © Spencer Hardy

Wonderous Willows

By Spencer Hardy

We all know “April showers bring May flowers,” but between the showers, April has its fair share of fascinating flowers. One of the most biologically interesting April flowers is also one of the most overlooked. Willow flowers begin as fuzzy white buds in late March and quickly become a pollen powerhouse that is crucial to many early season insects. While willow flowers are visited by many different insects, they are host to more species of specialist bees than any other plant genus in eastern North America. These specialist bees are only active during the spring bloom of willows and are dependent on willow pollen to provision their offspring. Check out the new willow page on the Vermont Wild Bee Survey website and learn more about the willow specialists in the state. Several of the species can be recognized from photos—see if you can find any this spring on your neighborhood willows!

11120, , white, , , image/jpeg,, 678, 645, Array, Array © Spencer Hardy
Eastern Whitelip © Spencer Hardy
11121, , white1, , , image/jpeg,, 1024, 768, Array, Array © jeffcherry (iNaturalist)
Eastern Whitelip © jeffcherry (iNaturalist)

Springtime Slime

By Julia Pupko

If I had to guess, I would say that you have probably heard the saying “April showers bring May flowers” at least once (perhaps in Spencer’s article above?). April showers bring something else too—terrestrial mollusk activity! Mollusks are a large group of invertebrates, encompassing both terrestrial and aquatic species, including: snails, slugs, bivalves (such as clams), octopi, squid, cuttlefish, and nautili.

Like many other terrestrial environments, forests have snails. In New England, one of our largest woodland snails is the Eastern Whitelip (Neohelix albolabris). Eastern Whitelips are difficult to find, as they are primarily nocturnal, spending their days in the leaf litter or tucked away in rock crevices. During winter, many woodland snails make themselves a burrow, using soil and leaf litter. They retreat deep into their shells, sealing off the opening with a thick mucus layer and dropping their heart rate to survive the harsh winter months. As the days warm and rain falls, the moisture and increased temperatures awakens the snails. Snails are important organisms, munching on decomposing leaf litter, logs, fungi, carcasses, and other decomposing matter, assisting nutrient cycling along the way. To dissolve the calcium carbonate in their meals, which is needed to build and maintain the snail’s shell, snails secrete a mucus with a high acid content.

Most snails require moist conditions to survive, and will go dormant during the warm season if conditions are dry, retreating into their shells and sealing the opening with mucus. Unfortunately, rain in New England is not always the friend of our snails. Acid rain eats away the calcium in forest decomposing matter and soils, which can reduce snail populations by as much as 80 percent!

As the weather continues to warm, and rain continues, snails will begin to mate. Most snail species are hermaphrodites, and some can self-fertilize when needed. However, most snails will still mate when possible. Snails are not particularly well-studied, so make sure to report any sightings you have to iNaturalist!

11125, , bobo, , , image/jpeg,, 768, 655, Array, Array © Nathaniel Sharp
Bobolink © Nathaniel Sharp
11123, , hermit, , , image/jpeg,, 1024, 678, Array, Array © Nathaniel Sharp
Hermit Thrush © Nathaniel Sharp

Early bird gets the… nocturnal migration?

By Julia Pupko

At approximately 11:34 PM, I received a text from my fellow housemate and VCE staff member, Kevin Tolan: “Hermit Thrush just flew over.” Now, there may be several questions coming to mind, such as “How did Kevin know there was a Hermit Thrush overhead?” and “What is a Hermit Thrush doing, zooming over their house in the middle of the night?!”

Although birds such as hawks, pelicans, falcons, hummingbirds, swifts, and swallows migrate during the day, many bird species actually migrate at night. Other species, both resident and migratory, along with mammals, amphibians, and invertebrates are primarily active at night, making it difficult to spot them. As a result, Kevin decided to set up an audio monitoring system out of his window, allowing him to better monitor the fauna surrounding and passing by our home. He set it up at the prime time, right before spring migration, giving us a chance to monitor bird species as they begin their nightly flights towards their breeding grounds.

Birds migrate at night for a number of reasons. First, the air is cooler and the atmosphere is more stable, making it easier for many species to stay on course. Cooler nighttime temperatures also reduce the chances that the birds will overheat. The cover of darkness decreases the number of predators that may snack on these flappy friends. Nighttime migrants rest and feed during the day, though some birds can rest half of their brain at a time, which allows them to partially sleep while flying. They often migrate in mixed flocks containing many different species. Anywhere from hundreds of thousands to millions of birds are traveling across nighttime North American skies during spring and fall migration.

As the migrants fly, many call to each other (cue Kevin’s nifty recording system). Researchers are not entirely certain why migrants call as they fly, however, there are some prevalent theories. Birds likely call to ensure that individual members of the flock are able to stick together and warn others about danger. Higher call rates have been observed when the weather is bad (making it harder for birds to stick together) and in areas where there are high collision rates with man-made structures, seeming like they are trying to warn the other birds of the imminent danger.

Lights may also be confusing to birds—at best, increasing the call rate of migrants and at worst, potentially causing increased migrant mortality (think lights in skyscrapers attracting birds towards a city-scape in the middle of the night). For example, an outdoor nighttime art-exhibit light show during peak migration in Pennsylvania was monitored by researchers to ensure that migrating birds were not negatively impacted by the display. They found that the birds were able to navigate past the display, but their call rate increased a lot, with six times the number of calls being recorded in the immediate vicinity of the structure as were recorded at another station, less than two miles away.

Migrating birds likely use a number of methods to migrate, such as astronomical bodies, the Earth’s magnetic fields, sense of smell, and likely others as well. The mechanisms of migrant navigation, especially of birds traveling on overcast nights, is still poorly understood. Birds also migrate in waves, with short-distance migrants (those that only migrate a small distance south to avoid the harsh Vermont winter), such as Red-winged Black Birds, arriving first. Other short- and medium-distance migrants, such as American Robins, Killdeer, Wood Ducks, and Eastern Phoebes are not far behind, arriving in March and April. The longer-distance migrants—many of which travel to the Caribbean, Central America, and South America—such as warblers, Eastern Wood-Pewees, and Bobolinks, arrive later, usually in late April through May.

You can observe nighttime migrating birds by setting up a scope towards the face of the moon on bright nights, and watch the birds flying past it. You can also listen for their flight calls. However, these calls take practice to differentiate and some are very difficult to hear. If you truly wish to invest, you can explore recording options and set one up at your house, like Kevin did. But you might want to think twice about texting your friends at midnight with news of your discoveries!

11126, , ostrich, , , image/jpeg,, 768, 1024, Array, Array © Nathaniel Sharp
Ostrich Fern Fiddleheads - those that are the most tightly furled can still be harvested © Nathaniel Sharp
11127, , ostrich2, , , image/jpeg,, 768, 1024, Array, Array © Nathaniel Sharp
Unfurling Ostrich Fern fiddleheads - past their harvestable time. © Nathaniel Sharp
11128, , ostrich3, , , image/jpeg,, 768, 1024, Array, Array © Kent McFarland
Ostrich Fern © Kent McFarland


By Julia Pupko

Warmer temperatures of early spring signal dormant plant life that it’s time to wake up–including our edible species! One tasty treat that will be popping up in the coming weeks are fiddleheads. Fiddleheads are the still-closed fronds of ferns, harvested soon after they push up from the soil, before they start to unfurl. There are two considerations when fiddlehead harvesting: 1) harvesting and preparing the correct ferns and 2) harvesting sustainably.

Not all ferns are edible: the species most commonly foraged in Vermont are Ostrich Ferns (Matteuccia struthiopteris). Ostrich Ferns have smooth, hairless stalks with a groove that runs from the base of the fern all the way up the stem of the frond. The fiddlehead itself will be bright green and will have some brown, papery scales on it. Five to seven fronds will come out of a central point, and vegetation from the previous year’s Ostrich Fern fronds can be found surrounding the fiddleheads. Ensue that you thoroughly cook the fiddleheads before consuming them—they contain trace amounts of toxins that can make some people ill (cooking removes these). Boiling for 10-15 minutes or frying thoroughly (recommend with garlic and butter!) does the trick.

It is important not to over-harvest when you go fiddlehead hunting. I try to steer away from harvesting fiddleheads on heavily-trafficked trails, where others are likely to harvest them. General rules, summarized from Robin Wall Kimmerer’s Braiding Sweetgrass, are to never take the first ones you find, only harvest from large patches, and never take more than half. Always leave a few fiddleheads in each individual clump, and if you notice someone has already taken some, do not harvest from that clump or in the same patch, depending on how much it has been harvested.

Fiddleheads are only good to harvest for a few days. I would recommend doing some additional research of your own before getting out there,  or better yet, taking a COVID-safe excursion with an experienced forager!

Comments (4)

  1. Gretchen McFarland says:

    Wonderful articles and great photography. Thanks!

  2. Scott Maclachlan says:

    We have cluster flies in early spring at our home. They seem to disappear quickly when our flycatchers and phoebes arrive.

  3. Larry Layne says:

    Thanks so much for another month of interesting notes and photos, this time of things to look for as spring unfolds. I was particularly struck by the photos of the cluster fly and of the white willow flower. I enjoyed the personal notes on bird migration and fiddleheads.

  4. Richard Martin says:

    Thank you for the great work.

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