What Do Warm Winter Temperatures Do to Insect Populations?

A common question we have been receiving in the Plant and Insect Diagnostic Clinic (PIDC) is if the warmer winter temperatures we have been experiencing in Iowa will result in increased insect and arthropod abundance this summer. Will there be more ticks? What about other insects like mosquitoes and boxelder bugs? Well, the short answer is it depends and remains to be seen for many. In addition, more than just temperature will have an impact on insect populations. Things like precipitation can also be a huge factor. Conditions will affect different species differently, and it’s impossible to know what to expect from every species.

Brown marmorated stink bug with an egg mass.

Insects have several mechanisms for surviving winter. Some migrate to warmer areas (monarch butterflies, for example). Others may stick around and rely on other strategies, like the biological “antifreeze” that insects have in their blood. This can allow survival even if temperatures drop well below freezing. Certainly, there are temperatures that are too cold and will cause death, but those temperatures aren’t always reached to an extent that will significantly impact insect populations (and on top of that, every species will have a slightly different lethal temperature that must be reached to cause death). So, it’s arguable that you can experience fewer of some insects after a very cold and long winter, but a warmer winter does not necessarily mean that we should expect the opposite.

In fact, I can think of more cases where warmer weather negatively impacts insects rather than benefitting them. Take brown marmorated stink bug for example, that can overwinter in our homes and human structures and become a nuisance. If it gets too warm during the winter, they can become active, use up fat/energy reserves before plants have emerged to provide additional food, and they can die if cold weather returns or if they starve from no food availability outside.

Inevitably, some species may do better after warm winters, and others may do worse. But if anything, warm and abnormal winters in Iowa probably have a net negative impact on insects, particularly when considering that a lot of insects are emerging (including pollinators and other beneficial insects) when there is no food available for them yet.

So, the short answer is that it is impossible to predict how every insect will respond to a warmer winter. But that is partly because we have not yet discovered every insect in Iowa, and we are far from understanding the biology of each individual species we have discovered and described. If you’re going hiking in warm weather and you’re worried about ticks or mosquitoes, it’s probably best to be proactive about them at any time, and not worry about them more just due to a warmer winter.

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