Where Do They Go

12/2021 Issue: Where Do Insects Go During Winter?

By:  John Moore, MSc Entomology

I was asked recently “Where do the insects go in the Winter”?  The simplest answer?

When the change in seasons means that you lose your resources (food and shelter), you have three very basic choices:  (Please select only one) A. Move (migrate), B. Die (adult form), or C. Sleep(diapause). Imagine having to make this decision every year until resources are available again.  (Please stay away from option B.)   The methods various insects and other arthropods use to accomplish any one of the methods of survival can be very complex.

Ants such as the Carpenter and Pavement ant will begin by eliminating all non-essential personnel (like males) that take up resources without contributing.  They may eat them or simply force them out of the colony.  Then they usually retreat deeper into the soil.  In the case of the Pavement ant, they huddle together covering whatever eggs or larvae might be present and remain still.  Movement requires energy and energy requires food or using up fat reserves.  Many ant species have a natural antifreeze to protect them from extreme cold.  However,  if the winter is too mild and they don’t get chilled down enough to reduce energy requirements, they will starve to death before spring.   In the case of the Carpenter Ant,  they will also rid themselves of non-essentials and gather in a tight group in a wood cavity or similar void and await being chilled down.  Similar strategy, sleep to eliminate the need for energy and wait for the return of resources.  Contrary to popular belief, if the winter is a mild one, ants tend to starve.  The same can be said if the winter is unusually cold or long.  In that case, the ants will freeze to death.

Moths and Butterflies use all three choices depending on the species.  The Monarch Butterfly migrates in great numbers to Central Mexico to “sleep” in the trees before migrating back to the north when the Milkweed begins to grow.  The Indian Meal Moth uses a very different strategy for survival.  Their survival process is called diapause.  As winter approaches and resources are limited, temperature and humidity are reducing, reproduction for the IMM is no longer possible.  During this change of season, the larvae (caterpillar) continue to develop until it reaches its last stage (instar) just before turning into an adult (moth).  Based upon the many different cues the insect is tuned into, such as temperature, humidity and light dark cycles, he/she will “pause” his continued development.  He/She spins a silken shelter and sleeps until the conditions are right the following spring.  Then he/she will complete his/her development and change into the adult Moth.  See the picture below where the temperature was 23°F and all were very much alive!

Stored product pest beetles such as the Cigarette Beetle and Warehouse Beetle also respond to these similar environmental cues of temperature, humidity reduction and light/dark cycles.  These changes trigger physiological changes in the insect that slow movement, reduce feeding and halt reproduction.  Three life stages of stored product pest beetles (egg, larvae, and adult) are very cold tolerant and capable of surviving some very cold temperatures.  They cannot reproduce or move at extreme cold, but they can survive the winter by using their “sleep” option.  If they can successfully be chilled down, they minimize their energy usage and rely on fat reserves until the time of year when temperature, light, and humidity are optimal again and resources return. 

Many species of Spiders also use the “sleep” method.  They only difference is in the life stage they choose to over winter.  Many spiders endure the cold and non-existent resources of winter in the egg sac stage.  In this stage, if they are sufficiently chilled, their development slows or even stops.  This reduces the need for energy.  The sac must be in an area that is sheltered with moderate humidity and temperatures between 30° and 40° F.  Other spiders like the long-lived Wolf Spider, seek out these same sorts of shelters.  This enables them to slow their metabolism and reduce energy needs.  They are then relying on fat reserves until the spring when resources are again available.  However, spiders also face the same risks as the insects mentioned.  If winter is too mild and energy needs are not reduced, they are likely to starve before spring.  So, here’s to the bugs!  May your winter be mild or harsh and short.

John Moore is a graduate of The Ohio State University and Corporate Director of IPM for FSS, Inc.