Garden Tips: How insects survive winter cold

Last week, we talked about how plants survive winter temperatures. This week, we will move on to how insects manage to survive in freezing weather.

Like plants, they have developed various strategies.

Avoiding the cold altogether is one way some insects survive. For example, the Monarch butterfly flies south to Mexico for the winter and returns the following year. This long trip is fraught with peril.

It is amazing that this butterfly still exists, but its numbers have seriously declined because of loss of its habitat, in particular the milkweed plant. Milkweed is the Monarch caterpillar’s only food source. The availability of this plant along the butterfly’s long journey has been greatly reduced because of more effective weed control along roadsides and on agricultural lands. To find out more about the Monarch’s decline, go to bit.ly/monarch_decline.

The other way insects avoid the cold is by finding a protected location where they can spend the winter. One example is the elm leaf beetle. As winter approaches, the adult beetle seeks a protected spot where it can spend the cold months. This spot can be under piles of leaves or other debris, but it can also be within the outside walls of homes that it enters through small cracks and crevices. The beetles spend the colder months inactive in a kind of dormant state and later and emerge from hiding in the spring as the weather warms. Once they emerge, they start looking for their food: the leaves of elm trees.

I wish cold weather would put an end to the nasty little stinging ants in my garden, but these guys simply close the opening to their nests and move deeper in the soil, protected by the insulating layer of soil above, as well as by any layers of snow or mulch.

Some insects survive winter because they are freeze-avoidant. They avoid injury from freezing temperatures by supercooling their body fluids. These are changes in their body chemistry that prevents the water in their body tissues from freezing. They can do this by producing sugars and polyol chemicals that act like antifreeze. This happens gradually as the weather cools in the fall.

Codling moth, an insect pest that attacks the fruit of apple and pear trees, is one example of a freeze-avoidant insect. The codling moth’s larvae spend the winter under the bark of trees. Because they can supercool their bodies, they are able to easily survive temperatures down to minus 10 degrees. A number of other insects that feed on trees and shrubs, such as aphids and adelgids, are also freeze-avoidant insects.

Another strategy involves allowing ice to form only outside of an insect’s cells and organs. This involves changes in the insect’s body chemistry and the production of ice-nucleating proteins that help control the freezing process. Wooly bear caterpillars and cockroaches are example of freeze-tolerant insects.

We can hope that this winter’s cold weather will diminish the number of insect pests we find in our landscape and garden, but it is unlikely. Just like plants, they have adapted and developed various strategies for surviving frigid temperatures.

This story was originally published January 1, 2017 at 3:09 PM with the headline "Garden Tips: How insects survive winter cold."