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Squirrels, chickadees and trees aren't the only things that live through the long, cold winter. Many insects and microorganisms can survive a Chicago winter just fine, according to Stephanie Adams, research specialist in plant health care at The Morton Arboretum in Lisle.
Some insects, including many solitary bees and wasps and even some butterflies, spend the winter as adults, tucked in "pretty much any nook or cranny," she says.
Take the mourning cloak butterfly: It folds its dark red wings and nestles into a crack in a building or a tree's bark. Then, like many insects, it replaces some of the water in its body with an antifreeze-like chemical and spends the winter in a state of frozen suspension. In early spring, it will warm up and flutter away. It's one of the first butterflies you'll see.
Other organisms overwinter at other stages of their life cycle, as insect eggs, nymphs, or larvae, Adams says. For example, the emerald ash borer spends most of the winter in its destructive larval stage, when it looks like a little worm. It's the larvae that tunnel in the wood beneath the bark of ash trees, cutting off water and killing them.
The larvae stop eating in winter, but they survive. In early spring, they begin the next stage of their life cycle, turning into pupae and then adult beetles, which can fly and lay eggs.
Overwintering insects are a boon for other forms of life. If you hear a woodpecker in winter, tap-tap-tapping in the treetops, it's hunting for adult insects or larvae beneath the bark.
Many insects and other invertebrates spend the winter in the soil or in the layer of leaf litter on top of the ground, where the debris shelters them. If it snows, that's added insulation.
For example, the tomato hornworm overwinters as a cocoon in the litter of the vegetable garden — one example of why it's wise to clean up the vegetable garden at the end of the growing season.
Bacteria and fungi can survive in the soil even if the first few inches are frozen. If you have a compost heap, you probably know that although it may freeze around the outside, it rarely turns entirely to ice. In the center of the pile, bacteria usually will still be alive and at work, consuming plant matter and generating enough warmth to keep the ice at bay.
Most kinds of fungi do useful work breaking down the leaves that fell in autumn and other plant material, while others can cause plant diseases. Fungi overwinter in a variety of forms, such as white threads called mycelia that you might see in soil or mulch or as microscopic reproductive pellets called spores.
The disease-causing fungi can survive the winter on infected branches and leaves, so it's best to clean them up and get them out of the garden. You can still finish your garden cleanup in winter, before it gets warm enough for disease-causing organisms to spread easily, according to Sharon Yiesla of the Plant Clinic manager at the Arboretum.
The winter is a slow time, but it's not lifeless. As you huddle against the cold on a February day, you may be ready for spring to come. But all around you, there are other forms of life that are ready too.
Beth Botts is a staff writer at The Morton Arboretum in Lisle (mortonarb.org). For tree and plant advice, contact the Arboretum's Plant Clinic (630-719-2424 or plantclinic@mortonarb.org).