Expert Column: How Grocers Can Keep Fall Pests Out of Their Stores


As we welcome the cool fall breeze and vibrant red and orange leaves, retailers need to be on the lookout for insect pests seeking a warm shelter for the winter.

Fall invaders, such as cluster flies, may try to sneak into grocery stores looking for a home to survive the winter. They often hide where no one can see them and frequently go unnoticed until they emerge in late winter or spring. By the time occasional invaders are recognized as a problem, the pest population may be fairly large, and it may be too late for simple control measures. That's why it's important to plan ahead and implement control efforts before cold temperatures drive these pests indoors.

These invaders typically don't pose any threats to humans or building structures; however, they can pester your customers and hurt your reputation. Following are some of the fall invaders to watch out for and tips to keep them out of your stores this fall.

Cluster Flies

Cluster flies are slightly larger and darker than the common housefly and move more sluggishly. These flies tend to appear in heavy concentrations on the sunny side of buildings during late fall and early winter, seeking warmth, and can also be seen buzzing and congregating around windows.

Their search for a warm place to survive winter may bring them to your buildings. Be aware that cluster flies are capable of crawling through small openings in screens, doors and walls to find a secluded place to hibernate, such as wall voids.

On sunny winter days, the wall voids where cluster flies hide can grow warm, causing them to think it's spring. If this happens, they may come out of hiding prematurely and move toward the light coming in through windows. They will then cluster around the inside of the windows trying to get back outside and can leave stains on walls if crushed.

Stink Bugs and Box Elder Bugs

Similar to cluster flies, stink bugs and box elder bugs begin looking for warmth this time of year, which is why they can often be found on the south- and west-facing walls of stores, where the sun hits. Consider taking extra precautions against their activity on south- and west-facing walls before they crawl inside.

While stink bugs and box elder bugs don't pose any serious health risks, they can make a big mess. Stink bugs are named for the smelly odor they produce when they’re threatened, and box elder bugs' droppings, which are reddish-orange in color, are unsightly and can leave stains behind.

Asian Lady Beetles

The Asian lady beetle –- commonly known as the ladybug –- was imported to the United States in 1916 and released into the wild to help reduce native aphid populations that can ruin crops and other types of vegetation. Unfortunately, they became a major pest themselves in many areas of the country.

Today, Asian lady beetles are common throughout most of the United States and parts of Canada. They occur in a wide spectrum of colors, ranging from yellow to orange to red, and have a varying number of spots.

In the fall, Asian lady beetles gather in large numbers on the outside of light-colored buildings. As they gather on walls, some find cracks or holes they can use to get inside. They hibernate through the winter and become active again in spring.

Fall Prevention Tips

Fall invaders can be difficult to control once inside, because their hiding places are scattered and hidden. And, because they stay hidden during winter, it's easy to forget they're there, until they suddenly emerge in late winter and spring trying to get back outside –- that's when they really become a problem. If you hire a pest management professional to kill these pests once they emerge, you risk the chance of attracting secondary pests -- species that are normally kept in check by natural enemies.

Fortunately, implementing integrated pest management (IPM) strategies throughout the year can keep these fall invaders out of your building. Plan ahead and implement control efforts before temperatures drop and drive these pests indoors, with these simple tactics:

  • Inspect the outside of your stores regularly and carefully. Look for any openings pests may use as entrances.
  • Check the weather stripping on all exterior doors.
  • Seal any cracks around doors with metal mesh and caulk.
  • Consider applying a residual product on the outside of buildings. When combined with the exclusion practices listed above, a residual can significantly help reduce the likelihood that these pests will come inside.
  • Use dark-colored paint on the outside of buildings, as occasional invaders are attracted to light-colored buildings.

These tactics should be part of your broader IPM program. Work with your pest management provider on setting up a proactive IPM plan for your store, which can help protect it from pests in any season.

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