What Attracts Stinkbugs to the Indoors?

Millions of brown marmorated stinkbugs, or BMSB, invade American homes every year. You probably wonder why these relentless critters are almost magically drawn to the indoors -- it's a purely natural attraction. Their passion to get inside your home is triggered by the fall equinox -- an intriguing astronomical event that also compels other insects, such as cluster flies and Asian lady beetles, to seek shelter. Once entrenched, they hibernate and spend the winter.

Two Stink bugs on xmas decorations
credit: Steven Heap/iStock/Getty Images
Brown marmorated stinkbugs migrate into homes on warm fall days.

Why There Are So Many

In Asia, where they originate, a species of wasp keeps stinkbugs nicely in check, but with no natural predators in the United States, the BMSB population is uncontrolled. They smell bad and taste worse, so other insects promptly spit them out at first bite. Although spiders and praying mantises dine on the foul-tasting creatures, they don't make a dent in their huge populations.

What Stink Is About

Hitherto unknown on the North American continent, the stinkbug, or Halyomorpha halys, was accidentally introduced into eastern Pennsylvania, wreaking havoc on agricultural crops and creeping out homeowners well before the first one was collected and identified in September 1998. This nearly 3/4-inch-long member of the insect family Pentatomidae is defined as a true bug and named for scent glands located on the dorsal surface of the abdomen and the underside of the thorax, filled with chemicals designed for defense. The presence of stink bugs may be less disturbing when you know they do not reproduce indoors. Although devastating to agriculture, they do not cause medical or economical harm to homeowners -- stinkbugs are simply a nuisance.

Fall Equinox Equals Stinkbugs

In the Northern Hemisphere, later dawns and earlier sunsets usher in cooler days as summer melts into winter. The fall equinox occurs late in the day on September 22, with its first full day on September 23. At this crucial juncture in the earth's rotation, nothing can stop the onslaught of stinkbugs. At this precise time, driven by sheer instinct, the bugs arrive. Casing homes for the southern side, but not craving warmth as you might expect, they look for the sunniest, warmest and most reflective areas. They squeeze through cracks and crevices in the brightest place they find, only to crawl into the coldest, darkest nooks and crannies to hibernate and survive the winter. On warm winter days or when exposed to a heat source, the bugs may move about. In spring, they emerge in full force, attempting to get back outside to start breeding and laying eggs.

Plants and Trees Stinkbugs Love

While you can't do much to change the course of nature, you can meet the formidable challenge stinkbugs present by caulking up cracks and crevices around windows and doors to limit entry points, and limiting plants and trees these stinky intruders find irresistible. According to extension tree fruit entomologist, Greg Krawczyk, the brown marmorated stinkbug feeds and develops on more than 300 different host plants. Just a few of the plants and trees stinkbugs love include: fruit trees like peach and apple; blackberries; butterfly bush (Buddleia davidii); tomatoes; ornamental millet; and sunflowers.