Leopards and tigers and bears!

Post by Jen Berlinghof

Around the first frost is the best time for spotting bears in the Lake County Forest Preserves in northern Illinois…woolly bears, that is! These fuzzy caterpillars succumb to a late fall wanderlust and can often be found traversing trails and roads, as well as climbing vegetation and nibbling a last few bites before winter sets in. They belong to the subfamily Arctiinae, commonly known as tiger moths. Their scientific name stems from the ancient Greek word arktos (“bear”), for the appearance of their hairy larvae.

A woolly bear caterpillar (Pyrrharctia isabella) found along the Des Plaines River Trail. Photo © Lake County Forest Preserves.

Any ten-year-old child can probably identify the most common woolly bear larva in the area, the isabella tiger moth (Pyrrharctia isabella). It boasts orange and black bristles in a banded pattern. That same child may also try to convince you this critter can predict the severity of the coming winter by looking at the length of the caterpillar’s bands of bristles. But just as groundhogs can’t truly predict the spring, moth larvae cannot predict the winter. After each molt, a stripe of the black setae (stiff hairs) is replaced by orange setae. This makes the orange band broadest in the last instar, or stage of larval development.

The author holds a giant leopard moth caterpillar (Hypercompe scribonia) in her hand. Photo © Lake County Forest Preserves.

I found another type of woolly bear caterpillar on a recent hike at Ryerson Woods (Riverwoods) that might be less familiar to folks. The larva of the giant leopard moth (Hypercompe scribonia) sports shiny black bristles separated by red inter-segments. Like the isabella moth larva, this giant woolly bear lacks stinging spines and doesn’t bite. When alarmed, it curls up into a tight ball, displaying its setae like little swords that can irritate the skin and mucous membranes of potential predators. This defensive posture also makes its bright red inter-segments prominent, a literal “red flag” to warn predators they’re unpalatable.

In its defensive posture, a giant leopard moth caterpillar displays its stiff setae and red inter-segments. Photo © Donald W. Hall.

Once these woolly bears have gorged themselves on asters, milkweed, sunflowers, violets, and even dandelions—and almost finished growing as larvae—they ramble on to find a suitable spot under leaves or logs to wait out the winter. Unlike most moth larvae that spend our freezing months tucked inside a pupal “sleeping bag,” in general tiger moths overwinter as nearly full-grown caterpillars, pumping glycerol through their bodies to keep their cells from freezing solid. They then emerge in spring to munch a bit more before creating a cocoon and completing metamorphosis.

The familiar orange-and-black woolly bear caterpillar emerges in spring as an adult isabella tiger moth. Photo © Patrick Randall.

An adult giant leopard moth. Photo © Christopher J. Williams.

As the sun sets earlier in the final days of fall and winter approaches, take these last moments to try to find these fascinating larvae before they hide away and press pause on their development. Discover new trails with our Hike Lake County Challenge before it ends on November 30. Then, come spring, look for the adult moths when both larvae and people emerge to explore the new season.

Surviving in the subnivean

This winter has been harsh in Lake County, Illinois, causing many of us to wish we could migrate to South America like some birds do, or hibernate in a cozy underground den like the groundhog.  Alas, most of us just stick it out in the cold. It may offer consolation to know we are not the only animals active during these record-breaking cold, snowy days. It turns out there is a whole ecosystem teeming with life right under the snow.

Recently, scientists having been taking a closer look at life in the subnivean, which literally translates to “a place under the snow.” The space between the snow and the ground acts as a seasonal refuge for invertebrates, birds, and small mammals. Snow affords these small critters with remarkable insulation, and temperatures around 32 F regardless of the temperature above the snow. Biologist Bernd Heinrich explains the science underlying these insulating properties in the book Winter World: The Ingenuity of Animal Survival. “As long as both ice and water exist side by side, they constitute a thermostat keeping temperatures constant.” When water converts to ice crystals, heat releases. When ice turns into water, the process uses up heat.

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