Nature Notes

Life on the Winter Prairie

By Holly Einess

At first glance the prairie in winter appears lifeless and rather bleak. The colorful flowers of summer and fall are absent, replaced by the dull golds and grays of dormant plants and trees.

bennett-johnson prairie trailBennett-Johnson Prairie Trail

However, to the careful observer the winter prairie reveals a world full of life and drama, albeit on a smaller scale, and has many stories to tell.

Way back in June (a distant memory on this January day!), a gall fly laid an egg on a goldenrod stem. The egg hatched into a larva that ate its way into the stem, and in response the plant created a ball gall. The larva lived inside the gall all summer, continuing to eat and grow until autumn, when its body started producing glycerol (a kind of antifreeze) and it entered diapause, the insect version of hibernation. There it would have remained until spring, when it would have transformed into a pupa and finally emerged from the gall as an adult fly. Unfortunately for this particular larva, it was discovered by a downy woodpecker or a chickadee, which knew that pecking a hole in the gall would likely yield a tasty snack.

goldenrod ball gallGoldenrod ball gall

In autumn wooly bear caterpillars are a common sight, crossing paths and sidewalks en-route to winter resting sites. But crawling along the snow on a January day? Why yes, entirely possible when the temperature is above freezing! The wooly bear is the larval stage of the isabella tiger moth. Unlike most butterflies and moths, it overwinters as a caterpillar, spinning its cocoon come spring.(Fun fact: ALL caterpillars become either butterflies or moths.)

wooly bear caterpillarWooly bear caterpillar

Like the gall fly larva, the wooly bear produces glycerol to help prevent its hemolymph (the insect equivalent of blood) from freezing. Rather than spending the winter in diapause, however, it does so in a state of quiescence; it can come out if its hibernation-like state when conditions warm, then return to it when the temperature drops again. And all those legs helping it move along? Only the front six are true legs (a characteristic all insects share); the others are called prolegs, small fleshy structures attached to the caterpillar’s abdominal segments.

The prairie plants themselves have life cycles too, of course, growing both from seed and from rootstock in the spring and lying dormant in winter.Today I identify thistle, goldenrod, sunflower, golden alexander, indigo, and mullein. Though far more showy when in flower, they retain a muted beauty in winter.

indigo seed podsIndigo seed pods

Leaving the prairie, I take the Wood Duck Trail back to the visitor center and can’t resist a peek at the bird feeders. There are chickadees in abundance, and I wonder if any of them had gall fly larvae as an appetizer!

black-capped chickadeeBlack-capped chickadee

Holly Einess is a Minnesota Master Naturalist Volunteer.

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