Overwintering State

In ecology, we often talk about the “overwintering state” of insects, animals, plants, and other living things. As we approach the end of February and Spring is on the horizon, I think perhaps it is not too depressing to talk about overwintering. We’ve almost made it, although Thursday night’s surprise 11” snowfall may have brought some doubts.

We woke Friday morning to discover that the predicted 3-5" of Spring snow had burgeoned to 11" and turned northeast Iowa into a winter wonderland! We still have a bit of overwintering left!

Plants have a variety of strategies for overwintering. Annual plants overwinter as seeds and start out new every year. Trees and perennials have a dormancy that allows their growing points (meristems) to remain alive, despite bitter cold. Sometimes only the roots and root crown overwinter, and the plant grows back from the base. Some plants, like the great waterleaf (Hydrophyllum appendiculatum), produce some leaves in the fall and throughout warmer opportunities during winter, so they’re ready to jump into action. Finding these lovely little patches of fresh green variegated leaves peeking out in the early Spring is such a delight. The trees will wake up gradually, and one of the first signs of this is when the sap starts to flow in the maples. This is a hydraulic process, where freezing and thawing cause vacuums and release of pressure in the water conducting tissues, so that sap is pulled from the roots up into the stem of the tree. This gives us maple syrup season! Generally, it needs to be below freezing at night and get above freezing during the day for maple sap to “run”; the conditions can be right for a series of day, then stop for a while because it is either too warm or too cold and then start again. That’s already happened this year: we had warm enough conditions 1.5 weeks ago for the sap to start to flow, then it got TOO warm, and now it is too cold again. But soon it will be just right, we hope. Then we will begin our maple syrup making demonstrations.  

Insects too have a variety of strategies to overwinter. Some overwinter as eggs, some as larvae, some as adults. The chemical composition of insect blood changes to forms that will resist formation of ice crystals. Mosquitoes have several overwintering stages, depending on the species. Many species of mosquitoes overwinter as eggs, but some species will hide out as adults in protected places (tree holes). Those are the ones we see so early in the Spring! Boring insects, like emerald ash borer (EAB), survive the winter beneath the tree bark. EAB often overwinter as pupae then emerge as adults in Spring to mate and lay eggs to start the cycle over again. Huge numbers of EAB larvae chewing away under the bark of an ash tree kills the tree. The woodpeckers eat many EAB, but they never get them all. When we have REALLY cold temperatures (below -20 °F), some of the overwintering EAB may die from the cold, but in Iowa it is never cold enough for long enough to really impact the population, and even if some die the population will rebound quickly. So you can’t count on our January cold snap to have saved us from EAB.

Our local animals have their own set of overwintering strategies. We see our deer and squirrels wearing a thicker coat as they are active all winter long. The chipmunks disappear into their burrows and spend the winter in a state of torpor with slower heartrate and temperature, waking every few days to snack on stored seeds. Our snakes go deep into the rocks and dens where they won’t freeze. And of course some of our birds just leave town. They change States, or even continents. Many of our summer songbirds are down in Central or South America for the winter. Our winter birds (cardinals, woodpeckers, finches, nuthatches, juncos, chickadees, sparrows, and more) seem content to hang around at my all-you-can-eat sunflower seed buffet! But I know my “poor starving birds” are also out and about feasting on wild seeds and EAB larvae!

As for humans, for some of us our overwintering state is Iowa, for others it is Arizona or Florida! We look forward to welcoming the snowbirds back to the Midwest. I’ve been here all winter, and it hasn’t been that bad. That’s probably because I have a lovely space to retreat to on cold winter days. There is certainly a peace to sitting by a crackling fire with a warm cup of tea while winter cold and winds rage outside, and to wandering down a trail of freshly fallen snow. I don’t mind my winter State, especially since I can usually avoid driving on icy roads.

I guess you could say that my overwintering state is also gratitude for the many blessings of living in this place. Every season brings its unique special things which we try to share through our various events and opportunities. We certainly enjoyed our recent pottery and soapmaking workshops. March is all about maple syrup. In April we are offering a mushroom cultivation workshop. In May, we’ll welcome Dwight Zietlow back to Iowisota to share his knowledge of making wildcrafted vinegars and oxymels. In June we will be welcoming Chris Hall to talk about the human history of the Mississippi River Valley. July will bring Samuel Thayer to us for another plant identification workshop. Over the next months, we will have some open nature saunters, private retreats, and weekends of accommodation during local community events. Keep watching the Iowisota website and Facebook page to learn about upcoming opportunities!