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Mallard ducks on a pond with colorful fall leaves in the background
Mallards in fall © K.P. McFarland

Field Guide to September 2020

By Vermont Center for Ecostudies September 2, 2020

One morning, you wake to a nip in the air, and notice subtle changes in the quality of the light. Suddenly, it’s September. High in the sky, Broad-winged Hawks kettle and Common Nighthawks peent as they whirl southward. And high in the trees, Fall Webworms busily build their sticky hammocks and munch on late-summer leaves. Down at eye-level, butterflies like Monarchs and Painted Ladies glide by on their way to warmer climes. There’s a lot going on this time of year, if you know where to look. Here is your field guide to life on the move, and some natural history tidbits to discover this fall.

10446, Common Nighthawk sitting on a branch during the day., Common Nighthawk - Susan Young public domain, Common Nighthawk. Photo by Susan Young / licensed under Public Domain Mark 1.0, , image/jpeg,, 2047, 1363, Array, Array Susan Young / licensed under Public Domain Mark 1.0
Common Nighthawk. Susan Young / licensed under Public Domain Mark 1.0
4820, , nighthawk in flight Bryce Bradford, Common Nighthawk in flight.  Photo Bryce Bradford -, , image/jpeg,, 2500, 1875, Array, Array © Bryce Bradford
Common Nighthawk in flight. © Bryce Bradford

Nighthawk Watching

Kent McFarland

On warm summer evenings in the breeding season in Vermont, Common Nighthawks once roamed the skies over treetops and towns. Their sharp, electric peent call was the first clue that they were overhead. At dusk, these long-winged birds flew in graceful loops, flashing white patches out past the bend of each wing as they chased insects. Those days are mostly gone now, but in August and September during migration, the careful observer can still witness their spectacular flight as they whirl southward on their autumn migration.

Although most often seen migrating at dusk here in Vermont, Common Nighthawks migrate at all hours of the day, often in large flocks, on one of the longest migration routes of any North American landbird. Many travel overland through Mexico and southward through Central America, while others pass through Florida and across to Cuba southward, flying over open water to reach their wintering grounds in South America thousands of miles away. Read more on the VCE blog.

Photo (left):
Photo (right):

10460, Fall Webworm nest, fallwebwormnestKPmcFarland, Fall Webworm nest © K.P. McFarland, , image/jpeg,, 1536, 2048, Array, Array © K.P. McFarland
A close-up of a Fall Webworm nest © K.P. McFarland
10459, Fall Webworms are everywhere, fallwebworm, Fall Webworms are everywhere. © K.P. McFarland, , image/jpeg,, 2310, 2310, Array, Array © K.P. McFarland
Fall Webworm caterpillars © K.P. McFarland
10461, Fall Webworm moths mating, fallwebwormmatingKPMcFarland, Fall Webworm moths, mating. © K.P. McFarland, , image/jpeg,, 2048, 1365, Array, Array © K.P. McFarland
Fall Webworm moths, mating on Kent's house. © K.P. McFarland

Worrisome Webs?

Kent McFarland

It’s the end of summer and they’re draped on the ends of tree limbs like some early Halloween decorations. Everyone is talking about them. Fall Webworm caterpillars are fattening up on leaves inside big bags of webbing on shade, fruit and ornamental trees.

Some tree-owners are worried. I’ve heard of people burning the bags, spraying, and cutting the branches off. But in most cases, this is much ado about nothing. The caterpillars are feeding on leaves that are near the end of their life. They don’t feed on the buds of next year’s leaves, so in spring new leaves will sprout with no sign of damage. The caterpillars usually don’t feed on the same branch or even in the same tree each year.  It is a native moth and it has more than 50 natural predators and 36 parasites that help keep populations in check.

Fall Webworms (Hyphantria cunea) are often confused with Eastern Tent Caterpillars (Malacosoma americanum). Fall Webworm nests are found in late summer and fall, while Eastern Tent Caterpillars appear in spring. Webworm nests enclose the ends of branches and the caterpillars feed inside the nest. Tent caterpillars construct a thick nest in forks of branches and only congregate in the nest at night or in inclement weather.

Fall Webworms overwinter as pupae in the soil. In June and July, the adult moths emerge and females begin laying their egg masses. The eggs begin to hatch in mid-July. Fall Webworms use over 90 species of deciduous trees as host plants. After feeding for a month or more inside the nest, they crawl down the tree, construct a cocoon, and pupate.

See more images of Fall Webworms and share your sightings at the Vermont Atlas of Life on iNaturalist.

Chicken of the Woods (Laetiporus sulphureus)  © marklisa91 licensed under CC-BY-NC
Chicken of the Woods (Laetiporus sulphureus) © marklisa91 licensed under CC-BY-NC

Fall Color on the Forest Floor

Spencer Hardy

The foliage fireworks of a hardwood forest in September are well known, but the explosion of color is not limited to the canopy. Beneath the rapidly accumulating leaf layer and in cracks of dead snags, there are short-lived bursts of blues, and sheets of orange brighter than any maple leaf.

After wet summers or the remnants of a hurricane, September can be a spectacular month for the fungiphile, with a wonderful diversity of shapes, colors and textures emerging from the forest floor, stumps, or even clapboards. So, on your next leaf-peeping outing, make sure to spend some time looking down, and don’t be afraid to get on your hands and knees to fully appreciate the subtle textures of the mushrooms and the many arthropods that are quick to colonize the fruiting bodies.

Vermont does have a number of edible species, but also several that are deadly poisonous, so unless you are a trained expert, it is best to appreciate the sights and smells and leave the eating to the beetles and flies. And in case you assumed plants were safer to forage for and eat than mushrooms, you should be aware that there are also several highly toxic plants that have been mistaken for edible ones.


9554, , Broad-winged Hawk calling, Broad-winged Hawk calling © K.P. McFarland, , image/jpeg,, 640, 960, Array, Array © K.P. McFarland
Broad-winged Hawk calling © K.P. McFarland
6078, , broad-winged-hawk, Broad-winged Hawk migrating. , , image/jpeg,, 864, 1121, Array, Array © Gerry Biron
Broad-winged Hawk migrating © Gerry Biron

Day by Day, Gliding Their Way to South America

Kent McFarland

While most migratory birds rely on full bellies to fuel their amazing journeys over land and sea, the Broad-winged Hawk relies on its soaring abilities. In fact, it wastes little energy on flapping at all. This hawk, like many others, is a glider. Using rising columns of hot air like an elevator, there can be hundreds, thousands, or even tens of thousands, in flocks or “kettles” slowly circling upward on a thermal and then gliding southward and downward to catch the next free ride. They rarely, if ever, sail over open water where few thermals exist, and they only migrate during the day. Instead, they follow the land as it gets narrower and narrower in Central America, eventually dumping some of them into South America after 40 days of migration.

These champions of migration are superbly adapted for the rigors of long distance flight: air filled bones to lighten the load, large and powerful hearts that are proportionally six times larger than a human heart, enhanced oxygen carrying capacity in their blood, a supercharged respiratory system using air sacs that allow fresh air to constantly bathe the lungs, feathers for flight and insulation, specialized pectoral muscles, and more.

This fall, climb a hill and watch the hawks glide southward one sunny day. Or, just before bedtime in a quiet place, go out and listen toward the sky. If you listen closely you will hear the waves of songbirds migrating overhead as they call to each other. Bear witness and wonder to the annual ritual that spans the eons and the globe—the mystery of migration.

Painted Lady butterfly nectaring on coneflower © Bryan Pfeiffer
Painted Lady butterfly nectaring on coneflower © Bryan Pfeiffer

Painted Ladies on the Move

Kent McFarland

Not elaborate Victorian-era houses, but butterflies. Painted Lady butterflies are flitting about fields, gardens, roadsides and meadows throughout eastern North America and beyond. Like Monarch butterflies, with which they are sometimes confused, Painted Ladies are now migrating southward. But where, exactly, are they going?

Each fall, these butterflies vacate Canada and most of the U.S., and during winter are active only in parts of the extreme southern U.S. and Mexico. When spring arrives, they push northward to breed, sometimes arriving in the Northeast in large numbers. But they’re not as predictable as Monarchs.

You can help us piece together this migratory puzzle with eButterfly checklisting. What’s that, you say? eButterfly users (you can become one, it’s easy and free!) submit complete checklists of all the butterflies they can identify and their effort expended in finding them. These checklists allow us to do a variety of interesting analyses. We can show where a species is found and where it hasn’t been reported. We can calculate the chances that a species will be found at a given time of year in certain locations. And most importantly, we can develop species distribution models that show these migrations across the continent.

Visit and add all of your butterfly checklists, with and without Painted Lady observations, every day this fall and help us unravel the mysteries to their migrations across North America!

10464, , A placata_simplex-Nathaniel Sharp, Goldenrod Cellophane Bee (Colletes solidaginis) © Nathaniel Sharp, , image/jpeg,, 768, 1024, Array, Array © Nathaniel Sharp
Mining Bee (Andrena placata/simplex) on Goldenrod © Nathaniel Sharp
10463, , C solidaginis-Nathaniel Sharp, Mining Bee (Andrena placata/simplex) on Goldenrod © Nathaniel Sharp, , image/jpeg,, 909, 1024, Array, Array © Nathaniel Sharp
Goldenrod Cellophane Bee (Colletes solidaginis) © Nathaniel Sharp

Late Summer Goldenrod Visitors

Nathaniel Sharp

Throughout late summer and early fall, fields and meadows in Vermont are aglow with the yellow blossoms of goldenrod. Many species of goldenrod, in the genus Solidago, can be found in Vermont. These common plants are often labeled as a weed and blamed for fall allergies, even though many more pollen grains are carried away on the specialized leg hairs (corbicula) of bees than are blown into nostrils by the wind.

Look closely at the sunny yellow, composite flowers of a goldenrod and you will often find them bursting with activity. From industrious, non-native Western Honey Bees, to many species of native bumblebees, to the alien-like, angular Jagged Ambush Bugs that lie in wait for their prey to stop by a flower. Many insects stop by goldenrods while they’re in bloom, but few only visit goldenrod, and the species that do specialize on this common plant are something to be on the lookout for in September.

The species featured in the photos above, the Goldenrod Cellophane Bee and a goldenrod-specific Mining Bee, share a fondness for goldenrod pollen and a habit of building their homes in loose, sandy soil. These bees collect pollen from a variety of goldenrods, which they use to feed their young back home in their underground burrows. If you find yourself in an area with sandy soils and lots of blooming goldenrod, see if you can find any of these adorable, fuzzy bees and photograph and upload them to the Vermont Atlas of Life on iNaturalist. This valuable data will also help us keep track of the many species of bees found in Vermont through the Vermont Wild Bee Survey, happy hunting!

Comments (7)

  1. Gretchen McFarland says:

    Well done!

  2. Emilie Daniel says:

    Very happy to read about Fall Webworm Caterpillars, I didn’t know any of this info. Thanks for the enlightenment!

  3. Larry Layne says:

    I look forward each month to read this email, especially The Field Guide for each month. I want
    to say thank you. I appreciate all your efforts.

  4. A beautiful, too quick tour.

  5. Marcia Haas says:

    I, too, look forward to the monthly field guide. I think it was July’s or August’s that talked about the evening primrose moth and after reading about it I found 3 at once on a wild evening primrose in our yard 🙂

  6. Kate Donahue says:

    Looking out for the hawk kettle. I will miss them,, though.

  7. Annette Seidenglanz says:

    Been posting mushrooms on my iNaturalist page and not getting any helpful suggestions. Any active groups that can help me? I have an interest in identifying species but I’m not a forager.

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