Wooly Bear Caterpillars

I found this little wooly bear asleep in the garden under a pile of fallen leaves and tucked it back in for the winter.

I miss the hum and activity of bees, butterflies and other insects that populate our garden. But, as I finished up some outdoor work, I was reminded that their absence is temporary. I spotted a familiar small, fuzzy form: a banded wooly bear caterpillar (Pyrrharctia isabella) asleep for the winter beneath some fallen leaves.

Though we usually call these little creatures wooly bears or wooly worms, there are more than 260 different species of them in North America. Each has a different coloration and becomes a distinct species of moth. The banded wooly bear is black on both ends with rusty orange in the middle. When the caterpillar reaches maturity, it becomes an Isabella tiger moth. Though I’ve seen many banded wooly bears, I have yet to see the moth, which is usually a muted orange, salmon or yellow color with black spots on its body and wings.

Wooly bears are generalists — they eat many types of plants including grass, clover and weeds. This one had just crossed the Lake Nokomis walking path in Minneapolis.

The banded wooly bear caterpillar grows up to 2 inches in length. Its fuzzy body is covered in tiny bristles called setae that are black on the caterpillar’s ends and rusty orange in the middle. The number of orange segments increases as the caterpillar grows. Though a few people might be sensitive to the bristles, most have no problems handling the caterpillars. I remember carrying them around as a child and holding them with our toddler son on nature walks. 

Is it true that the size of a wooly bear’s orange band predicts the quality of the winter ahead? No, according to the sources that I read (please see the list below). Explanations include: the size of the orange band increases as the caterpillar grows; those with more orange grew up in a drier habitat and those with more black segments grew up where it was moister; lots of variety occurs naturally among caterpillar populations; and there’s plenty of disagreement among all of these views. In spite of the arguments, it’s fun to observe, compare and chart the size of wooly bears bands — especially with children!

Banded wooly bears in Canada and the northern United States typically produce one brood each year, though two generations are possible. Those that hatch in August feed until late autumn. They eat a broad range of grass, weeds and wildflowers, and aren’t crop pests. In autumn, they enter quiescence (a type of insect dormancy) for the winter, usually in leaf litter, or under a log or rock. 

Look for wooly bears on sunny, mild autumn days. This one crossed the Sakatah Singing Hills Trail in southern Minnesota.

How do they survive our harsh winter? They produce a cryoprotectant,¹ an antifreeze to prevent cells from rupturing when they repeatedly freeze and thaw. The bristles or setae also help the caterpillar to freeze on the outside first, protecting the inner organs. In the spring, each caterpillar will awaken from quiescence, resume feeding and spin its cocoon. About two weeks later, an adult Isabella tiger moth will emerge.

Banded wooly bears range throughout the United States, Canada and even into Mexico. You might catch a glimpse of them feeding in the spring, but it’s more likely that you’ll spot one in autumn when you’re out walking, biking, or working in your garden.

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Sources List for Further Reading

The Infinite Spider Blog 

Minnesota Department of Natural Resources

NPR Science Friday video

National Weather Service

Scientific American Blog

University of Wisconsin – Milwaukee: Bug of the Week Blog

¹The cryoprotectant is produced by other wooly bear species, too. In fact, the Arctic wooly bear (Gynaephora groenlandica) caterpillar has a life cycle that stretches over seven or more years! The Arctic summers are so brief that the caterpillars must feed and enter quiescence repeatedly for several years before gaining enough biomass to metamorphose into a moth. Overall, they spend 90 percent of their lives dormant and frozen! (For more about the Arctic wooly bear, follow the link above to the Scientific American Blog.)

Gray Tree Frogs

This tiny gray tree frog’s green camouflage helps hide it in nature. (All of the tree frogs for this post were photographed by my sister in her garden.)

Like tiny amphibious chameleons, gray tree frogs (Hyla versicolor) change color to match their surroundings. Sometimes bark-like gray or brown, at times a leafy green, and at others a mottled combination of color that mimics lichens or rocks, these tiny frogs elude predators through camouflage. Sometimes they even display a shade of creamy white or tan. No matter what color they exhibit, all gray tree frogs have bright yellow or orange marks under their thighs.

Why are they “tree” frogs rather than just frogs? All species known as tree frogs (or treefrogs) have large toe pads that enable them to climb trees, sides of buildings, and other structures. Climbing trees is all about catching the wide variety of food available there on warm summer nights: small insects and their larvae, spiders, mites, aphids, snails and even smaller frogs. At night gray tree frogs also climb sides of houses to perch on windows and capture small moths and other insects attracted to light. Because gray tree frogs are nocturnal, I often hear rather than see them unless they perch on the windows. What preys on them? Small mammals such as skunks, raccoons and opossums. Snakes, birds and larger frogs also eat them.

Artificial lights attract gray tree frogs in search of insects. This little one climbed the side of the house.

Gray tree frogs typically inhabit woodland edges and gardens near water. We’ve seen them at our cabin in rural Minnesota, and my sister, who lives in a Twin Cities suburb, has regulars that hang out in her garden. They pop up in damp places — the cat’s water dish, inside her garden watering can, under flower pots, on the patio furniture and in her small fountain. Adults are typically found higher up in trees or shrubs, while younger tree frogs are more terrestrial.

This tree frog’s golden color blends well with the potted plant.
Gray and charcoal hues help camouflage a tree frog on this weathered deck.

Unlike most frogs, the gray tree frog sounds more like a bird as it trills its one-note call. They breed from April to July and call most frequently during May and June, though it can be as early as April and as late as September. Females lay their eggs near a shallow pond or pool of water. Hatching and development takes about 7-8 weeks. They reach adulthood in two years and the average life span ranges from 5 to 7 years. Adult size is generally 1-to-2 inches (3-to-5 cm) in length.

Tree frogs hibernate on land, usually buried under leaf litter, fallen logs and other materials. Their bodies produce glycerol, which is converted to glucose. Large amounts of glucose in the frog’s vital organs acts as an antifreeze. Ice crystals will form in the body cavity and under the skin, but the lungs and heart are protected from freezing, and stop functioning until spring. Warm weather will thaw the frog and it will revive and continue its life. Gray tree frogs live in eastern North America from New Brunswick to Manitoba, south to northern Florida and west to central Texas.

Young gray tree frogs are often bright green.

Further Reading

Gray Tree Frog – Minnesota DNR

Gray Tree Frog – New Hampshire PBS

Gray Tree Frog – NatureWatch

Early Spring Native Flowers: Bloodroot

One of Minnesota’s earliest native wildflowers is bloodroot, (Sanguinea canadensis). Given its name, you might expect a scarlet or crimson flower. In fact, it blooms ice-white with a sun-gold center, though some emerge light pink. They look out of place, so stark and fresh among the remains of last year’s woodland growth and garden detritus. Its name refers to the toxic red-orange sap in the rhizome or root.

Each bloom emerges wrapped in a single curling leaf like a little blanket. The leaf remains curled until the blossom withers and then unfurls into a rounded leaf with a varying number of lobes. The leaves range in color from light green to blue-green depending on the plant’s age and condition. In its natural setting, bloodroot often grows along woodland edges, which provide sun in early spring and shade when the trees leaf out. In my garden, it grows along the edge of an arbor vitae hedge and under an ash tree. With shade and regular watering, bloodroot creates a pretty ground cover that lasts all summer under deciduous trees. If they aren’t watered during summer’s hot, dry spells, bloodroot leaves just go dormant until the following spring.

Native bees, honey bees and beetles pollinate bloodroot, which also can self-pollinate. Fertilized flowers form elongated capsules that enclose spherical seeds colored black, red, or brown. Here’s what’s special about bloodroot seeds: Each produces an elaiosome, an attachment containing lipids, amino acids and other nutrients. Attracted to these nutrients, ants carry the seeds back to their nests and feed the elaiosomes to their larvae. The ants either discard the remaining seed in a separate chamber of their nest, or toss it back out onto the ground. Either way, this process, called myrmecochory, helps ensure that the bloodroot seeds are dispersed for germination. Other spring wildflowers, such as violets, trilliums, hepaticas and Canada wild ginger, also form this mutual relationship with ants.

A member of the poppy family, bloodroot is native to much of eastern North America from Nova Scotia south to Florida, west to Manitoba and south to Texas. Native Americans used the plant’s red sap to make paint and to dye clothing, leather and other items. It blooms from March to May in Minnesota woodlands and was one of the first native wildflowers that I identified in the woods at our cabin years ago. The plants in most of these photos grow in our backyard. They hold special meaning for me because they were a gift from my aunt, who grew them under her trees for decades. They remind me of how she nurtured my love for nature when I was young.

Further reading:

Ants as Seed Dispersers

Friends of the Wildflower Garden – Bloodroot

Minnesota Board of Water and Soil Resources – Bloodroot

Wisconsin Horticulture – Bloodroot

Spring Happens All Around Us

On a recent morning, a friend looked outside and noticed the green blush beginning on trees and bushes. She recalled a teaching colleague’s comment during playground duty years ago. The colleague, a quiet woman of few words said, joyfully, “Oh, take a look! Spring is happening right before our eyes!”

Indeed it is. Thunderstorms, rain and mild temperatures coaxed baby leaves from their snug buds. They open like tiny green roses, flawless and smooth, not yet chewed upon by insects or mammals. Even on these cloudy, gray days buds and baby leaves paint the landscape in soft pastel greens and yellows. Don’t miss their fleeting, fragile beauty! They’ll quickly mature to full size and summer’s cool greens.

Maple Flowers

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In Minnesota, native maple trees typically flower before bees and other pollinators are active.

Spring’s earliest flowers are popping open: gauzy crocus clusters, squill — Siberian and striped — and snowdrops that have bloomed through snow, cold and high winds for a month. They are lovely, these Eurasian transplants that paint the earth with pockets of bright color. Our native blooms are more hidden and less showy, yet are beautiful in their unflowerlike forms.

Look up at the maple trees. Easy to miss high overhead, these blossoms are small, muted and less recognizable as flowers. Each emerges from a scarlet bud coat and glitters with golden, translucent filaments tipped in auburn pollen. They remind me of minute, single-celled creatures that we might see in a drop of water under a microscope, or of the tiny squiggly animals living on a coral reef — beauty suspended in air rather than water.

silvermaplecaron

Male flowers of the silver maple (Acer saccharinum) are packed with pollen for wind dispersal.

 

The female flowers of red maples (Acer rubrum) remind me of tiny coral reef creatures.

Oh, and even if we don’t notice the flowers overhead, if you are allergic to tree pollen, your “nose knows” that maples are blooming! Why do they disperse so much pollen? In most years, maples and a few other trees bloom before native bees and honey bees are active. The early-flowering trees depend on indirect wind pollination. Male flowers produce copious pollen to successfully fertilize female flowers on other maples.

Who Will Nest Here?

Black-capped chickadees, downy woodpeckers and white-breasted nuthatches recently explored this cavity in our apple tree.

Our beacon apple tree is pushing 80 years old. It’s dropped a few limbs over time; some splintered under the weight of apples, others weakened with age and rot. One old limb bears a small cavity. “So what?” you think —  unless you’re a chickadee, nuthatch or other cavity dweller looking for a nesting site. All three species frequently explore and tussle over this cavity, and I believe the chickadees are winning.

One sunny, frigid afternoon, a downy woodpecker pair ducked in and out of the cavity and were confronted and chased away by a black-capped chickadee. A curious white-breasted nuthatch also sidled over for a peek and was waved off by the chickadee. Later, three chickadees fluttered around the opening until two chased off the third. The remaining pair excavated and removed wood chips from the cavity interior; evidence they are preparing a nesting site! The male sings his territorial “fee-bee” (sometimes “fee-bee-bee”) song. I first heard him sing on December 31. 

One member of the black-capped chickadee pair (Poecile atricapillus) removes wood chips from the apple tree cavity.

Chickadees deposit excavated wood chips away from the nest site to avoid leaving signs for predators.

Will this pair nest in our apple tree? Black-capped chickadees prepare multiple nesting sites before the female chooses one, so we won’t know for a few weeks. Wherever they nest, the female will line the tree cavity with moss, soft plant fibers, feathers, hair and fur. She will lay 1-13 (usually 6-8) white eggs marked with reddish-brown spots. The female incubates the eggs and the male feeds her on the nest. Once the hatchlings are old enough to be alone for a short time, both parents feed them. Insects (including their eggs and caterpillars) and spiders comprise most of their high-protein summer diet. Black-capped chickadees also eat other small invertebrates, seeds, nuts and berries. They’ll visit seed and suet feeders in the winter. One cold afternoon, as I topped off our sunflower seed feeder, a cheeky chickadee landed on the edge of my filling-cup, snatched a seed off the top and flew into our arbor vitae hedge to either eat its treat, or cache it for another day.

Black-capped chickadees remain in Minnesota year round.  They are common in much of the northern United States and most of Canada.

I enjoy the chickadees’ curiosity, high-energy antics and their melodious breeding calls, especially as winter drags on. Stay tuned to find out whether or not they nest in our apple tree.

Further Reading

Black-capped Chickadee; Audubon Bird Guide

Chickadee Delight. The Sleepy Eye Herald-Dispatch. February 3, 2020.

Haupt, Lyanda Lynn. The Urban Bestiary: Encountering the Everyday Wild. (First edition). New York: Little, Brown and Company, 2013.

November Honey Bees and Asters

A honey bee (Apis mellifera) nectars in asters (Aster novi-belgii) on a summer-like November day.

Two weeks ago, temperatures bottomed out at 15°F and a winter storm buried gardens, yards and colorful-leafed trees under almost 10 inches of snow. Now, sun and a week of daytime highs around 74°F have awakened chipmunks, spurred American robins to sing and enticed honey bees from their hives. The bees found our last asters of the season. In a sunny location, and protected by an overhanging arbor vitae hedge on the north side, the pastel blossoms continue to open despite the early snow and frigid cold. What a gift — a sweet treat for the honey bees and an unexpected return to autumn beauty for us.

Butterfly Sampler

A painted lady (Vanessa cardui) basks in the sun on a roadside rock to warm its flight muscles.

Like miniature floating tapestries —  stippled, spotted and striped — they decorate gardens, yards and roadsides. Butterflies are plentiful this summer. Alongside the bumblebees, they pollinate many flower species and aid with seed production. But honestly, I love them more for their color, grace and elusiveness; for the joy they evoke in the eyes of children and the hearts of people of all ages. I delight in the first and last of every season — often a mourning cloak or red admiral in late April and a tortoise shell or red admiral in October.

Here are a few of the butterflies I’ve seen recently:

Eastern-tailed blues (Everes comyntas) are active May – September in the Upper Midwest and southern Canada.

This hackberry emperor (Asterocampa celtis) was attracted by sweet apple juice in my pail of apple windfalls.

Mourning cloaks (Nymphalis antiopa) overwinter as adults and are often the first butterfly active in April. They favor oak and maple sap; watch for them at woodpecker drill holes.

Two rows of yellow spots on the forewing distinguish the black swallowtail (Papilio polyxenes) from the eastern tiger swallowtail female dark form (Papilio glaucus).

This female monarch (Danaus plexippus) deposits an egg on the underside of a common milkweed leaf.

White admirals (Limenitis arthemis arthemis) are common in areas with aspen and birch. They prefer sap over flower nectar.

Red-spotted purples (Limenitis arthemis astyanax) are a southern subspecies of white admirals and the two often hybridize in the Upper Midwest. This one’s wings show that it has survived a bird attack.

Banded hairstreaks (Satyrium calanus) lay their eggs on oak trees. This adult rests on common milkweed in our garden.

Eastern tiger swallowtails (Papilio glaucus) favor nectar from Joe-Pye weed, blazing star and phlox.

Red admirals (Vanessa atalanta) migrate north in April and usually depart in October. Their caterpillars feed on nettles.

Black Eastern Tiger Swallowtail

An eastern tiger swallowtail black form female nectars on nepeta ‘Walker’s low.’

It’s late spring with the entire summer ahead of us. Nature’s greens are deep and full. Tiger swallowtails (Papilio glaucous) are on the wing now, the first of two times during the Minnesota summer. The first flight is typically in May-June and the second in July-August. The offspring of the second flight overwinter in their chrysalides.

I watch a bright yellow male patrolling his territory, repeating the same route through the large silver maples across the alleyway, over our apple tree and under my neighbor’s birch tree. He is quick to give chase to other males that trespass.

Eastern tiger swallowtail males are always yellow with black stripes and lack the wash of blue on the hind wings.

On this sunny, breezy morning, a black form female nectars in a sea of blue nepeta in our front garden. Her iridescent blue-on-black wings flutter repeatedly from one end of the garden to the other. She is full of energy and free of wing tatters and tears.

The female’s underwings are marked with bright orange spots and light blue scales.

Most eastern tiger swallowtails in Minnesota are yellow with black stripes. However, the female is dimorphic, or appears in two forms: the familiar black-striped yellow and a rarer black form washed with shimmering blue across its hind wings. Faint black stripes are often visible on the dark female.

Just a tiny percentage of females appear in the black form, especially this far north, but are  common in the southern United States. Why? Scientists think that the black form is a mimic of the pipevine swallowtail, which tastes horrible because the caterpillars feed solely on pipevine plants. (Think of monarchs and viceroys, another example of mimicry. Birds hate the taste of monarchs because they eat milkweed. Viceroys closely resemble monarchs, so birds often avoid them.) Pipevine swallowtails occasionally come as far north as Minnesota.

Interested in attracting eastern tiger swallowtails to your yard or garden? Favorite caterpillar foods include: chokecherry, ash, poplar, maple, apple and mountain ash. Adults nectar on many flower species including phlox, milkweed, Joe-Pye weed, blazing star, bee balm/bergamot and red clover.

Violets Aren’t Always Violet!

As a youngster, I thought violets should be just one color: the shade of Crayola violet in my crayon box. In fact, violet flowers aren’t always violet! Many are blue, shades of purple, white and even yellow. The native common violet, or wooly blue violet, grows in almost every Minnesota county and in most of the eastern United States and Canada. It’s what many of us picture when we think “violet” (excluding African violets, which are a different plant family altogether).

The common violet or wooly violet (Viola sororia) blooms from April to June in the eastern United States and Canada.

Violets are a sure sign of spring in Minnesota and bloom from April to June. You’ll often find them in woodlands, thickets, gardens, lawns, along roadsides and even growing in sidewalk cracks. Individual species of violets can be tricky to identify and botanists disagree on how to classify them. Many of the backyard and roadside violets are common violets (Viola sororia), which may be blue, purple or white. The downy yellow violet (Viola pubescens) is also common in most Minnesota counties. It differs from many violets in that the flower stem arises from the leaf axil instead of growing separately from the corm.

The white form of the common violet clearly shows the pollinator “honey guides” on the bottom petal.

This violet came from my mom’s garden. I’d never seen violets this shade and loved them.

The downy yellow violet’s (Viola pubescens) stems and undersides of leaves are covered in soft, downy hair.

A typical native violet has heart-shaped or circular leaves with rounded teeth. In most species, the flower stem grows directly from the corm, which is similar to a bulb. Each leafless stem holds a single five-petaled flower. The purple-veined area on the lower petal is a nectar guide for pollinators. Bees see ultraviolet light and scientists think that the enhanced pattern visible to their eyes helps lead them to the nectar. In early May, typical pollinators are mason bees, tiny sweat bees and skipper butterflies. But, because the early spring weather can be cold and pollinators may be inactive, violets produce a second type of flower called a cleistogamous flower that doesn’t open. It self-pollinates and forms a seed capsule that ripens, bursts and ejects small brown seeds away from the plant. These flowers don’t form until after the trees leaf out. Look for them underneath violet plants later in the summer.

The violet plant is an important host for the caterpillars of many species of fritillary butterflies. Just as monarch larvae feed solely on milkweed plants, most fritillary caterpillars feed only on violets. Humans can eat violet blossoms, but not the rest of the plant, which is toxic. The blossoms provide vitamins A and C. In earlier times, they were used to make a simple, sweet jelly that’s also beautiful. To learn how to make violet jelly, and about other ways the flowers were used, visit PBS Wisconsin’s “The Wisconsin Gardener” for a brief, interesting interview.

Many fritillary caterpillars feed only on violets. This adult great-spangled fritillary (Speyeria cybele)  nectars on pink bergamot.

Violets sometimes form patches, especially in a garden or lawn. They are a good ground cover in shady places where grass does’t grow well. If you have too many growing for your liking, they are easy to remove. Just make sure that you pull out the entire root — and please consider leaving a few for early pollinators and for fritillary caterpillars to eat!