When arctic fronts, Alberta clippers, and the sinking jet stream begin to bombard Illinois, usually entering the northwest corner and sweeping diagonally across the state, it’s time to think about dusting off the cross-country skis, keeping the home pantry well stocked, or even planning that “spontaneous” trip south for the winter. As biologists, though, we take a different view of winter and see it as an opportunity to look for changes in animal life that have evolved over the millennia that allow them to cope with midwestern winters. Many of their activities are familiar to most—mammals hibernate, birds migrate, some organisms simply die off. But other organisms, some familiar, others not, take full advantage of an Illinois winter.

Winter Scorpionfly

Winter scorpionfly on moss.
If there’s one thing most people are thankful for each winter, it’s probably that insects, except for the occasional roach scurrying across a kitchen counter, are absent from their lives. But are they really? An obscure, bizarre insect that lives only in extreme southwestern Illinois, the winter scorpionfly, may just change your mind.

Scorpionflies (order Mecoptera), insects that aren’t really flies or scorpions, are an ancient group that traces its family tree back nearly 300 million years. In today’s world, however, relatively few species exist, only about 500; these are considered to be some of the most primitive insects that undergo complete metamorphosis. Eighteen species of scorpionflies live in Illinois. The most often encountered scorpionflies have small bodies with bright yellow-orange wings with black spots and horse-shaped heads. They are often seen sitting on foliage in humid woods each summer. For the more observant, consider the bizarre hangingflies. These slender-bodied predators, also with a horse-shaped head, hang by their front legs from foliage and trap prey with their hind legs.

The prize, however, if not for the most charismatic lifestyle, then certainly for the most hardy, must go to the winter scorpionfly. This diminutive denizen of mossy patches in the Ozark region of Union, Jackson, and Alexander counties is a true winter insect. Adults emerge from November to May and are thought to feed on moss. The easiest way to observe winter scorpionflies is to look closely at snow near patches of moss. The small (less than 5 mm long), dark dots cavorting around on the snow are most likely winter scorpionflies. Their wings are very small, and they are well adapted to living in cold areas (most species are found in high mountains or the far north). Their tiny wings mean they cannot fly. If you should happen to encounter a winter scorpionfly, not that this eventuality is likely to occur on any sort of a regular basis, it will be easy to identify. Illinois has only a single winter species (Boreus sp.).

Winter scorpionflies find suitable habitat in this ravine in far Southern Illinois.

Butterflies in Winter

Top, Buckeye; Center left, Giant swallowtai chrysalis; Center right, Question mark; Bottom, Mourning cloak.
What happens to butterflies in winter? These seemingly delicate, ephemeral creatures have devised several strategies for surviving during the long, cold months of an Illinois winter. The angular, multi-hued leaves, blown about by the cool winds of late autumn, may remind us of the recent past, of the colorful butterflies sailing across the spring and summer landscape, propelled by gentle, warm winds. With the advent of shorter days and cooler temperatures, though, these ephemeral spectors of warmer times vanish. Clues to their apparent magical disppearance, however, can be found in the massing together of monarchs on clear, fall days; in the presence of partially to fully mature caterpillars on dying food plants; or in the sudden appearance of a tattered butterfly on a warm, sunny day
in January.

Certainly, the most straightforward method to deal with winter is to head south. Only a single Illinois butterfly species employs this tactic—the familiar monarch. Illinois monarchs group together each fall and head south for central Mexico to spend the winter. These migrants are not the ones that came north the previous year, but their children, grandchildren, and great-grandchildren. Most make it through the winter and head north in spring, laying eggs as they go. Some make it all the way to Illinois to lay eggs for a new crop of monarchs. Others do not, and it is these succeeding generations that complete this remarkable journey.

A caterpillar that is fully grown in late summer or early fall will likely spend the winter as a leaf-brown chrysalis, attached to the stem of its last meal, to emerge with the warmth of spring, replete with an unblemished scaly covering. Employing yet another strategy, the viceroy spends the winter as a partially grown caterpillar, rolled up in a leaf attached to its food plant. Other butterflies spend the winter as adults, usually hidden under loose bark, or in any appropriate crack or crevice. These individuals are not true hibernators, as they will rouse on warm, winter days. It’s not too unusual to see a battered mourning cloak flitting about in the weak winter sun, a premonition of things to come. Some species, such as the painted lady, cloudless sulfur, and buckeye, rarely survive an Illinois winter and must enter Illinois each spring to reproduce and eventually colonize nearly every county.

Winter Stoneflies

Winter stonefly.
The life of fall and winter stoneflies is another exception to the rule that insect activity ceases with the approach of cold weather. Twenty species of the state’s 65 native stoneflies appear from November through March. With a habit of congregating in places exposed to the warming of the sun’s rays, one can see them crawling about on exposed tree trunks, fence posts, or on rocks located close to a stream. The concrete bridges characteristic of Illinois’ highways are a beacon of warmth to a stonefly. Stoneflies belong to the insect order Plecoptera. In appearance, stoneflies are about a half an inch in size, have two pairs of wings, and are rather drab in color. The adults, although terrestrial, are seldom found far from water. They are poor fliers and crawling is the preferred mode of transportation. The eggs and nymphs are aquatic. The nymphs are often found under stones in streams, hence the common name—stonefly. The nymphs of the winter stoneflies are chiefly plant feeders. The adults feed on blue-green algae, or not at all. Nymphs emerge from the water, find a suitable perch, and metamorphose into an adult. The adults mate, lay eggs, and die, usually living less than a month. The entire life cycle is complete in a year. Although sunbathing in Illinois from November through March generally lacks appeal to most humans, the bridges over creeks emptying into the Middle Fork of the Vermilion River, or the clear rocky streams of southern Illinois, are perfect places to absorb the fleeting sunlight of winter and to see these most unusual Illinois insects, winter stoneflies.

Bay Creek at Bell Smith Springs Recreation Area in Pope County is a good place to find winter stoneflies.

Canada Geese in Illinois

In most areas of today’s Illinois, the knife-sharp wedges of Canada geese can fill the late afternoon sky of just about any midwinter day. The ancestral overwintering grounds of geese in the central North American flyway, however, were the rivers and floodplains of the Mississippi, Ohio, and Cache rivers. With changes in habitat availability, particularly impoundment lakes and agricultural land, most geese now congregate on a series of state and federal wildlife refuges across southern Illinois: Rend Lake, Crab Orchard Lake, Horseshoe Lake, and Union County Conservation Area. A count by wildlife biologists during most any January may reveal around 500,000 geese in southern Illinois. While the migration of geese from the northland is an annual event, it’s not one to necessarily set one’s watch by. In some years, most geese arrive late, around the end of December. Because of mild weather conditions, they may extend their traditional stopover in southern Wisconsin. Geese need very cold weather and at least 10 to 20 inches of snow cover to trigger their southward trek. But, it is the lack of open land for foraging and open water, not the cold, per se, that triggers the migration.

During the hunting season, which runs from late November to mid-January, geese are very aware of state hunting statutes. Many a hunter wends his or her way home at the end of a day in the cold with only a memory of being serenaded by geese that were “just over the line” in an adjacent refuge. Once hunting season ends, the geese soon scatter across the state, feeding in corn stubble, and occupying just about any available lake, pond, or wetland. Make no mistake in assuming that only humans profit from an education. A naive, but alive, goose sporting Leopold’s proverbial “buckshot-battered pinions” has just learned an important lesson and may likely be next year’s honker, just out of shotgun range, murmuring in the neighboring wildlife refuge.

During the late afternoon, Canada geese fly in to feed din corn stubble at Emiquon National Wildlife Refuge near Havana.

Where Do Fish Go in Winter?

While gliding across the frozen surface of a lake in the middle of winter on silver skates, you probably don’t stop to consider where all the fish are. Perhaps on your return to that same spot next spring, after landing a particularly choice, hand-sized bluegill, obviously at least a year old, you might pause to reflect: Where do fish go when the temperature plummets and ice forms each winter? The answer is rather simple—they don’t go anywhere. Fish luck out because of a unique feature of ice—it floats. Water works the exact opposite of other liquids; it freezes from the top down, forming an insulating layer that actually allows the bottom of a lake or pond to remain liquid. Most lakes never freeze completely, and thus the fish can survive all year long. Anyone who braves the cold for ice fishing will tell you there are plenty of fish around.

Ice can cause a completely different problem for river fish. Though it is extremely hard for flowing water to freeze, it often does. Small bits of ice fall into the water and provide a place for more water to freeze. The ice particles then attach to solid objects and create ice caverns that disguise the fish’s familiar habitat. Sometimes, large ice flows are created that dam up the stream and
temporarily divert the water from the main channel. The next morning the sun melts the ice, leaving any hapless fish that have wandered into the diverted channel trapped in quickly drying pools where they will soon be prey for mammals or birds. In Illinois’ larger rivers, however, ice really does not cause much
of a problem. 

Fish in the smaller creeks, though, often face a major dilemma.  With all of the water tied up in snow or ice on land, creeks lose their water source and some dry up completely. Many fish are left stranded in drying pools; others, such as the Mississippi silvery minnow, are able to escape downstream where there is still enough water to survive. The spring cavefish, however, does the complete opposite. When the springs in which it lives in southern Illinois begin to dry, the cavefish moves upstream instead of down. It heads into the caves carved by the springs where there is always water and survives until the spring. Not only does the cavefish survive, it thrives during the winter and actually spawns. Each female presumably holds the eggs and the young in her gill cavity until they are old enough to fend for themselves.

Mississippi silvery minnow.
The Mississippi silvery minnow can be found in rivers and streams that have stretches of sandy bottoms, such as the Sangamon River.

Great Horned Owl Nesting Season

Great horned owl.
The woodpeckers are drumming, cardinals are courtship feeding, and woodcocks are concentrating on their aerial displays. These are the ornithological harbingers of spring, as our resident birds begin their nesting seasons. While it will be months before the Neotropical migrant birds begin to nest, those species that have toughed out the long Illinois winter are rewarded with the first choice in nesting sites.

One of the most spectacular of these early nesting birds is the great horned owl. Each year, before the last snows of winter have melted, these magnificent predators will choose nesting sites and lay two to three eggs. With cold winter weather still upon them, the eggs must be constantly brooded on all but the warmest winter days. The eggs will be incubated for about 4 weeks. Once hatched, the young remain in the nest, unable to fly for 10 to 12 weeks. During this time, great horned owls are prolific hunters, reportedly depleting local populations of small mammals in just a short time. The lack of green foliage increases the success of winter hunting and has been cited as the primary reason for the early nesting season of the great horned owl. By beginning so early, great horned owls can fledge their young from the nest before the vegetation becomes too thick and prey become difficult to find.

Great horned owls often nest in natural cavities of large trees.
Not particularly fussy in their nesting habits, these largest of Illinois owls often use old, red-tailed hawk nests or abandoned squirrel nests. Numerous pairs of great horned owls are observed nesting in Illinois each year.

Certainly, winter is not an easy time for any of Illinois’ animals as they face many dangers. Take heart in the fact, though, that as you skate over the ice, or drive past an Illinois stream, snuggle next to the fire with a good book, or sit waiting patiently in a hunting blind, all around you the creatures of Illinois are living out their lives in pretty much the same way they have since the glaciers covered Illinois.

Michael R. Jeffords is a senior professional scientist with the Illinois Natural History Survey at Champaign and serves as the education and outreach coordinator. Susan L. Post is the staff writer for The Illinois Steward. Charles Helm is a retired entomologist with the Illinois Natural History Survey at Champaign.