Green Darner Migration

Common green darner female (Anax junius)

On a windy, warm September evening, the sun has set; the air is soft and dusky. Migration is underway, but not the avian sort. A few large common green darner dragonflies zigzag beneath the trees hawking insects. I look skyward and far above me, a river of swarming green darners surges — hundreds of them — straight south ahead of a cold front.

Born in Minnesota, these green darners migrate to the Gulf Coast of the southern United States and Mexico. When they arrive, they’ll mate and lay eggs to produce the next generation, which will migrate north in April or May. When they arrive here, they will mate and give rise to a new generation before dying. These progeny will hatch by late August and continue the cycle of migration and reproduction. 

But that’s not the entire story! Common green darners are present in the north all summer — so where did they come from? There’s a resident population that doesn’t migrate. They’re active and deposit eggs throughout the summer and autumn. However, their young, called naiads, won’t mature until the following spring. They will wait out the winter on the bottom of a pond, marsh or slow-moving river or stream.

Averaging 3 inches in length, and with a wingspan of 3.5 inches, green darners are among our largest dragonflies. This one also is a female. Males’ abdomens are bright blue.

Green darner adults eat mosquitoes, midges and other flying insects. The aquatic naiads feast on mosquito larvae and other aquatic insects, tadpoles and tiny fish. Green darners are eaten by spiders, large robber flies and birds such as kestrels.

Further Reading

Mead, Kurt. (2009). Dragonflies of the North Woods. Duluth, Minnesota: Kollath & Stensaas Publishing.

Smithsonian Magazine

UW-Milwaukee Field Station

Hidden Music Maker

Katydids’ green bodies are easily mistaken for plant leaves. Can you spot one under the flower on the right?

Walk outside and listen on a late-summer or early autumn evening. Insect music has replaced the chorus of robins, mourning doves, northern cardinals and other birds. The new songsters might include tree and field crickets, cicadas, grasshoppers and katydids.

Unlike their more somber-colored cricket cousins, katydids are often bright green and are well camouflaged by plant leaves and stems. Very long antennae and wings held vertically over the body distinguish them from grasshoppers. Many could pass for a small leaf on a plant! I often hear katydids calling, but rarely see them.

Similar to their cricket kin, katydids create sound by rapidly moving the sharp edge of one wing against a ridge of bumps on the other wing — this is called stridulation. Each species creates a different sound. Most produce clicks, rattles or buzzes that differ in pitch, pattern and volume. Only one species, the common true katydid (Pterophylla camellifolia) “says” its name. (The link includes both group and individual recordings.)

Katydids’ ears are located below the knee joint. Zoom in to see the small, dark oval shapes called tympanum.

Katydids have narrow hearing organs located below each knee on their front legs. Though the location differs from mammalian ears, the ear structure is similar to our own. Simply put, sound waves cause a katydid’s eardrums to vibrate. The vibrations rock a small plate that transmits sound waves to the auditory vesicle, which contains fluid. The waves move through the fluid over tiny sensory cells that glean information and send electrical impulses to the katydid’s brain. Scientists theorize that locating a mate and avoiding predators are two key purposes of katydid hearing.

What eats katydids? Owls, kestrels, other birds, rodents, tree frogs, insects and spiders prey on them. Mainly vegetarians, katydids eat leaves and flowers of plants, but sometimes eat insects — including other katydids!

Next time you’re outside in the evening, listen for katydid calls. Crickets aren’t the only nighttime musicians!

Further Reading

Katydids – Wisconsin Horticulture

Katydids – Tettigoniidae

Songs of Insects

Only This Moment

White-tailed doe (Odocoileus virginianus)

The eyes of a white-tailed deer are liquid and deep. Walking at a nature preserve, I sense and then spot a doe’s motionless face gazing at me from a dry creek bed. We stand alert and silent. Though I don’t see them, a young fawn or two are probably hidden nearby waiting for their mother’s signal to move. Birdsong, the wind and children’s voices in the distance fade away behind the curtain of green foliage. There is only this place and moment.

Skimmer Dragonflies

Male widow skimmers (Libellula luctuosa) are dark brown with a bluish frost called pruinose.

What do you think of when you hear the term skimmer? A shore bird, a kitchen utensil, or perhaps a type of shoe? Skimmer also refers to the earth’s largest family of dragonflies, Libellulidae

Skimmers might be the image that many envision when they “think dragonfly.” Skimmers’ wings are large and patterned with spots — usually black and a powdery grayish-white. Like all dragonflies, skimmers hold their wings spread out horizontally from the body when resting. The head is large with eyes that contact each other on top. Two inches is a common body length, but it can vary between one and three inches. Adult skimmers dine on many soft-bodied insects, especially mosquitoes, flies, small moths and winged ants. Nymphs, or immature dragonflies, develop underwater where they eat mosquito larvae, fly larvae and other aquatic organisms. Skimmers are preyed upon by raccoons, skunks, shrews, bats, turtles, snakes, frogs, fish, spiders, larger insects such as praying mantids, and many bird species.

A female twelve-spotted skimmer (Libellula pulchella) perches on a dead forb in an urban oak savanna.

The twelve-spotted skimmer (Libellula pulchella) and the widow skimmer (Libellula luctuosa) are two common skimmers of Minnesota. Though similar in appearance and size (about two inches long), the difference is in their wing spots. Male twelve-spots carry 12 black patches and eight white spots between the black ones. Male widow skimmers show a dark black wing patch from the wing’s base to about midwing. One large white spot extends outward from the black patch. Female and young juvenile males of both species only exhibit black patches. Males and females of both species are coppery brown, but adult males develop a whitish-blue dusty or frosted appearance, called pruinose, on the abdomen. Both species sport bright, neatly etched side stripes — yellow in twelve-spots and orangish in widow skimmers. In addition, the thoraxes of mature twelve-spotted skimmers display two yellow stripes. 

Why the name widow skimmer? One explanation is that most male dragonflies carefully guard their mates during egg-laying, but widow skimmer females deposit their eggs unguarded, and thus became commonly known as widows. Another is that the black wing patches were thought to be reminiscent of a widow’s shawl.

A female widow skimmer’s wings show the black pattern reminiscent of a widow’s shawl.

Both skimmer species may be found near ponds, lakes and marshes, but they also venture away from water into fields and meadows. I observed two twelve-spotted skimmers in a small area of oak savanna in Saint Paul, about three city blocks away from a pond. One perched on a dead tree limb, the other atop a dried up forb, wings spread horizontally and glistening in the sun. 

Though not the most eye-catching of dragonflies, I like them; they’re easy to observe because they often forage in open areas away from water and remain close to their conspicuous perches. Both species share a similar geographic area. Twelve-spots range throughout most of southern Canada, the continental United States and northern Mexico. Widow skimmers occur in southern Manitoba, Ontario, Quebec and Nova Scotia, across the United States, except for the Rocky Mountain region, and in a portion of northern Mexico. Both skimmer species are on the wing during the summer months and the twelve-spotted skimmer is active through September.

Further Reading

Minnesota Dragonfly: Twelve-spotted Skimmer

Minnesota Dragonfly: Widow Skimmer

Seashore Early Morning

Early morning on a Gulf Coast beach in West Central Florida.

Early on there is the sound of seabirds and surf, the scent of sand and salt with a hint of fish. Steel-blue water surges inward tossing up sea jewels with names like cockle, calico scallop, cat’s paw, coquina and lucina on the sand before it retreats in a quiet hiss.

Willets, sanderlings, terns and other tiny shorebirds race ahead of the surf on their skinny legs. They probe the wet sand for breakfast invertebrates after each retreating wave. In contrast, brown pelicans swoop in soundlessly over the water. One plunges sharply, surfaces with a fish that squirms as the pelican swallows. On shore, a great blue heron stands companionably near a fisherman, waiting for the catch of the day.

Sanderlings (Calidris alba)

Royal terns (Thalasseus maximus)

A few feet from shore, the rising sun lights up sea oxeye daisies, blanket flowers, dune sunflowers, seaside gentians, sea oats, sea grapes and other native plants. They help anchor the dunes and provide habitat for many insects, birds and other creatures.

Seaside gentian (Eustoma exaltatum)

Florida west coast dune sunflower (Helianthus debilis vestitus)

Blanket flower (Gaillardia pulchella)

They are lovely, but it is to the sea that I return; sea and open sky. The rhythmic swoosh and hiss, ebb and flow, lulls, relaxes, and focuses me on this present moment. It is peaceful, joyful, hopeful. A fresh start.

Kentucky Coffee Tree

Kentucky coffee trees form thick, leathery pods that reman on the tree during the winter.

Walk down Twin Cities’ streets and look at the trees. June berries grow next to basswoods, red maples with hackberries and crab apples. The single-species plantings of the past are being replaced with a broad mix of native species and more resilient hybrids.

The Kentucky coffee tree (Gymnocladus dioicus) is one such native that’s interesting in appearance and history. The tree’s dark pods, open branch structure and scaly bark caught my eye because they differ from the smooth, gray-barked basswoods and red maples growing nearby.

The scaly, craggy bark of Kentucky coffee trees sets them apart from trees with smooth, gray bark, such as basswoods and red maples.

I didn’t think that a tree with Kentucky as part of its name would survive so far north, but it’s native to several counties south of the Twin Cities and new cultivars grow well north of the cities. It is listed as being native to Ontario, Canada, and the Central United States from Pennsylvania west to Nebraska and from Minnesota south to Oklahoma. It typically grows in small clusters because, in spite of its large seeds, it spreads mainly by forming suckers or root sprouts. The tough, impermeable seed coats result in a low germination rate. You’re more likely to find it growing on a city boulevard than in the woods. As a result, in Minnesota, the Kentucky coffee tree is listed as a “species of special concern.”

Female Kentucky coffee trees develop large green pods that darken in late summer.

The ripe seed pods contain several marble-sized seeds, which are toxic unless thoroughly cooked.

Like locust trees, the Kentucky coffee tree is a member of the pea or legume family, but its pods are large, reddish-brown, woody and thick compared to its relatives’, which are much slimmer. Whitish-green male and female flowers grow on separate trees. The fertilized female flowers form light green pods that ripen to the dark coloration in autumn. The tough pods contain several marble-sized seeds surrounded by sticky pulp and remain on the trees through winter. Native trees prefer rich, moist soil near rivers, but above the flood plain.

How did a tree in the pea family garner the name coffee tree? Early Kentucky settlers thought the seeds resembled coffee beans, but there’s no relation between the tree types. According to several sources, settlers roasted the seeds and used them to brew a coffee substitute — but don’t brew your own! They stopped this practice as soon as coffee could be imported because the beverage tastes very bitter — and unless they are thoroughly roasted, the seeds and pods are toxic!

This young Kentucky coffee tree shows the full foliage and green seed pods of summer.

Further Reading:

Minnesota Department of Natural Resources

Eloise Butler Wildflower Garden

University of Kentucky Department of Horticulture

Autumn Nostalgia

It rained leaves yesterday: red and silver maple, elm and basswood. Ash and birch fell last week. Other maples, oak, aspen, hackberry and ginkgo are still to come. The sky was hazy sun, the air windy and mild. A few late asters bloomed and honey bees jostled each other seeking the season’s last pollen and nectar. I am nostalgic for another summer gone by and I do not look forward to winter. 

The leaves kindle warm memories of the past: Nighttime walks scuffling through dried leaves with family and friends; autumn bonfires, years of after-school leaf walks with our young son. His warm, small hand held mine and his other was packed with leaves for projects — leaf bouquets, nature collages and little booklets with leaves and seeds of neighborhood trees. 

I miss the leaves; every year it’s the same. I miss their spicy scent, earthy and tangy with just a touch of sweetness as they break down. I miss their nighttime whispers on warm, summer winds, and the rattle of older, dry leaves in autumn. November winds whip them into swirling, airborne eddies and send them skittering down streets. They catch among rocks and old stalks, tucking in our garden until spring. Summer’s green umbrella slowly smolders to yellow, orange, russet, red and maroon. The canopy thins and falls, nestling woodlands and yards under a colorful quilt for winter.

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.

wooly-bear-caterpillar-tom-2

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

Robins and Apple Blossoms

Spotting a robin in March signaled the onset of spring to me as a child. We had a “Golden Book” titled, Birds: A Child’s First Book About Our Most Familiar Birds. It featured drawings of neatly woven nests cradling delicate eggs and portraits of familiar garden birds. Illustrations often showed robin nests built in blossoming apple trees and that image, along with the robin’s melodic songs, became synonymous with spring in my young mind.

Decades later, my husband and I bought our home in Saint Paul. Our first evening there, we sat on the back stoop beneath a beacon apple tree that’s now more than 80 years old. Two adult robins flew in and out of its leafy crown indicating the presence of a nest. A chorus of high-pitched chirps greeted the parents as the hatchlings anticipated dinner, their tiny heads stretching over the nest’s rim. During the next few weeks, we were privy to nestling squabbles, flight training, food procuring and the proper way to down a worm!

Some say that red-winged blackbirds (Agelaius phoeniceus) are the new sign of spring’s return to Minnesota. Robins now winter in the state and I hear their sweet songs on milder midwinter days. Many birds can withstand very cold weather as long as they find enough food to fuel their metabolic rate. Gardens often feature crabapple, mountain ash, dogwood and other fruit eaten by wintering birds. City boulevard plantings include fruit trees and larger trees like hackberry. I frequently see large groups of wintering robins dart between the crowns of boulevard hackberries near Saint Catherine University in Saint Paul. Robins also eat bird feeder food during winter that they wouldn’t touch in other seasons. Many a robin has dined with the woodpeckers at our suet feeder!

Sometimes I wake up to robin song drifting in through my bedroom windows in the predawn darkness. I remember childhood mornings of their pure, lovely caroling along with the scent of lilacs, the touch of humid air and perhaps thunder rumbling in the distance from an early morning storm. These are joyful memories — and though robins often ride out the winter in Minnesota, their clear singing, and the beauty of apple blossoms, still signify spring to me.

Further Reading:

American Robin

Red-winged Blackbird