As I sit at my laptop, typing this week’s “Gardening Corner,” I feel grateful for my cozy sweatshirt, yoga pants, and warm, fuzzy socks. The view from my window is bleak and barren. Sunny areas of the field where the snow and ice have melted are carpeted with brown leaves interspersed with white patches where snow has settled around the tree trunks. Jim’s raised vegetable beds and the shady half of the field are still covered with snow and ice.
In January, I wrote a column about the ways mammals survive the long, cold winter months by migrating, entering a state of dormancy, or adaptation. Today I can’t help thinking about the insects hidden away in frozen limbo underground and other places. Do they survive winter weather by similar methods?
The answer is yes; insects have developed various ways to survive freezing weather, despite the fact that they are cold-blooded and can’t produce their own body heat.
Monarchs and some other butterflies migrate south to escape the cold temperatures and return in the spring to complete their life cycles. Some species of insect pests don’t migrate south and will die from the cold, which may sound like a good thing, but while they are perishing from freezing temperatures, the same species in warmer climates will reproduce throughout the year. Their one or two new generations will migrate north in the spring to replenish the pest brigade. We will always have earworms, leafhoppers, and various species of aphids.
Many insect species enter a state of diapause in winter, a kind of suspended animation in which body functions and development slow down or cease until the soil begins to warm. Insects can enter diapause during any stage of development. When the temperatures begin to rise in spring, these insects will resume development as eggs, larvae, pupae, or adults. Think about all those white grubs you dig up in the spring; they will develop into the cute, colorful Japanese beetles that devour your roses in June.
Other insects adapt to cold temperatures in a variety of ways. These insects are more likely to survive when low temperatures are constant rather than fluctuating between freezing and thawing. They can survive in protected areas like sheds and barns, or in fallen leaves, brush piles, and firewood. The current plea to “leave the leaves” for pollinators developed with the realization that we are losing millions of beneficial pollinators and other insects every year with our long-held habit of cleaning up the garden at the end of the growing season. Many species of pollinators will lay their eggs or find a protected species in the hollow stems of garden perennials.
Insects that burrow into the soil for the winter have a good chance of surviving until spring because the underground temperature, protected by the cover of soil and snow, rises and falls more slowly than the air temperature, thus providing a more stable environment.
Other insects are considered freeze-avoidant or freeze-tolerant. Their body cells have developed other ways to prevent death from freezing.
Freeze-avoidant insects accumulate specific carbohydrates in their cells that act as antifreeze by lowering the freezing point of cell fluid. The sugar alcohols glycerol and mannitol are two of the carbohydrates that help some insects survive during the winter.
Freeze-tolerant insects have evolved to survive the formation and expansion of ice crystals in their bodies. The ice crystals form rapidly and cause body cells to rupture, leading to death. These insects produce specific proteins that control the freezing process, allowing ice to form in the spaces around body cells, rather than in the cells themselves.
Even on the most frigid winter days, there is life in, around, and under the surface of the garden, where insects are surviving and waiting for the lengthening days and rising temperatures that signal the appearance of springtime.
See Michigan State Extension publication “How Insects Survive Cold: The Potential Effect of a Mild Winter.”