Fall's Home Insect InvasionCrisp mornings and cozy evenings by the fire are welcome signs of the autumn season. But fall also signals the start of home insect invasions – not so welcome.

In temperate regions of the country, as days shorten and temperatures tumble, insects begin to seek out winter quarters. In warmer regions, as dry seasons fade to wet, insects shift into gear to search for dry quarters. While you anticipate spending the coming season snug, warm and dry indoors, insects are also eyeing your home as a potential winter haven.

As insects begin to squeeze, hop and crawl their way into your home, realize that the invasion isn’t personal. Simply put, insects are opportunists. They’re seeking shelter from winter cold, rains and snow. An open door, a crack between siding panels, a loose screen, or any opening in your home extends an invitation for your house to become a hibernation spot.

Once inside your home, insects pass the winter in a state of semi-dormancy known as diapause. They hang out in this resting state in wall voids, crawl spaces or attics.

What’s Behind the Exodus?

Several seasonal events trigger annual insect movements. The two biggest clues insects are wired to perceive are day length and temperature. Shorter days and cooler air signal that it’s time to acquire winter lodging. Even soil-dwelling insects, like grubs in your lawn, receive the “word” to migrate deeper into soil. Their clue is soil temperature – as soil gets cooler, the insects dig down a few more inches.

In warmer climes, the advent of the rainy season often sounds the starting bell for the annual insect race indoors. In California’s Central Valley, the first rains spark the invasion of tule ground beetles. In Texas, annual cricket mating migrations are tied to fall rains, which soften soil for egg laying.

Why My House?

Several reasons – and some known only to the insects – cause these creatures to choose your home.

  • It’s not unusual for insects to congregate – by the thousands – on west- or south-facing walls. These walls retain the sun’s heat and warm cold insect bodies.
  • Certain hues attract certain insects. Stinkbugs and cluster flies, for example, tend to gather on light-colored surfaces.
  • Ground beetles tend to infest homes that have planting beds located next to the foundation.
  • Box elder bugs frequent homes with yards that have female box elder and maple (especially silver maple) trees, the summer food source for these insects.
  • Millipedes migrate from moist, heavily mulched flower beds to moist basements.
  • In warmer climes, ants and roaches tend to wander in as weather shifts into autumn mode.
  • When insects hibernate in your home, scientists suspect they leave behind chemical attractants that call subsequent generations to gather.

The other reason insects may choose your home is simply because they don’t differentiate well between the bark of a tree and your cedar (or even vinyl) siding. Both have overlapping pieces that provide crevices ideal for passing winter. In an insect brain, both provide equal shelter.