Douglas A. Spilker, Ph.D., is a consulting ornamental plant pathologist and entomologist, garden writer and lecturer. Dr. Doug can be reached at

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Fall Invaders
by Douglas A. Spilker, Ph.D.    

It happens every year when the nights start getting cold — pests come crawling into your house from every nook and cranny. Here is a look at several home invaders and what to do to deter them.

Autumn is a wonderful time of year, with colorful leaves and invigorating cool weather. However, for many pests the change in season signals the need to seek shelter from the cold winter ahead. Whether they are insects, spiders or arthropods, occasional invaders typically live and reproduce outdoors. When indoor conditions are better for them than the outdoors, they invade structures, sometimes in large numbers. Most are harmless, or even beneficial as predators, but others can bite, produce foul odors or leave stains or damage books and furnishings.

Lady beetles eat plant pests including aphids, mealy bugs and scale insects, but become major annoyances when they assemble in large numbers.

Annoying Congregations

In early fall, direct chemical sprays to foundation walls and around potential pest entry points such as window and door frames, vents and where utility lines enter.

The most notorious fall invader is the adult boxelder bug, recognizable by its black color with reddish or orange markings. Boxelder bugs get their name because they are often found on boxelder trees. In autumn, boxelder bugs will amass on the sunny sides of rocks, trees and buildings and strive to enter any crack or gap in the structure to overwinter. When smashed, boxelder bugs may leave a reddish orange stain on walls, drapes and other fabrics.

The brown marmorated stink bug has now spread from the Mid-Atlantic states to the Midwest. The shield-shaped adults are brown to gray with marble-like (marmorated) coloration, and release a foul odor when disturbed or crushed. They feed especially on fruits and other crops and congregate in fall just like boxelder bugs. 

Besides being colorful, lady beetles are beneficial because they consume plant pests including aphids, mealy bugs and scale insects. However, several species, including the multicolored Asian lady beetle, have become major annoyances when they assemble in large numbers. If disturbed or crushed, the beetles secrete a foul-smelling orange-colored fluid that can stain fabrics, carpeting and walls. They are known to nip human skin.

Ants: Number ONE!

Ants are the number-one pest reported by homeowners, according to a survey by the National Pest Management Association (2010). Ants are the scourge of homeowners as they invade kitchens looking for food and water, especially during warm months. Ants may also be attracted to your home as they protect and care for honeydew-producing insects, such as aphids, soft scales, whiteflies and mealy bugs, on your landscape plants. Spraying or pruning infested plants close to the house may eliminate the ant problem. Otherwise, ant control can be a challenge that requires a two-pronged approach using indoor baits with a perimeter pest control spray.

As these bugs and beetles gather on structures in the fall, disperse them with strong water sprays or pesticide treatments to keep them from releasing chemical scents that attract more insects to the site. If they have already entered a home, use a vacuum cleaner to collect them. Remove the bag to prevent them from escaping or leaving a foul odor. In areas with a history of problems, preventive pesticide sprays should be made in late summer or fall just prior to insect congregation.

Moisture Lovers

Several non-insect pests, such as pillbugs and centipedes, normally live outdoors in damp places like under rocks, leaves and in mulch. When conditions are not suitable outdoors, they enter homes in search of moisture, food and shelter. Pillbugs (sowbugs, roly-polies) are not insects but crustaceans, gray to brown with seven pairs of legs. Pillbugs invade structures, but do no damage and commonly die of desiccation once inside. 

Probably the most unnerving pest is the house centipede, a long-legged and fast running predator of insects and spiders. Exclude these multi-legged pests by inspecting and sealing foundations, and deter them by reducing moisture indoors and outdoors, especially in areas where mulch is against the house.

Silverfish tend to hide from humans, which means their damage may also go unnoticed.

Silverfish are quick moving insects, with a silvery, metallic appearance and fish-like shape, typically found in moist, humid areas, such as bathrooms, basements, garages and attics. If silverfish are seen, consider a dehumidifier for your home, and look to repair dripping faucets and wet wood. Since silverfish feed on paper, book glue and clothing, do not store these items in areas where silverfish are normally found. Professional pesticide applications may be necessary especially if attics get infested.  

Not So Itsy-Bitsy

Common house spiders and cellar spiders “daddy-long-legs” commonly pose no threats to humans. Inside structures, spiders are most likely to be found in upper corners, window frames, under furniture and in basements and garages. Most spiders and their webs are just a nuisance, but a black widow spider bite can cause severe pain. Black widow spiders spin their webs near ground level, so use caution before putting your hands in areas with webs especially in protected areas such as garages and wood piles. If webs, egg sacs and spiders are particularly bothersome, use a vacuum cleaner to remove them. If a broom is used, adults usually escape. 

Black widow spiders are most recognized by the red hourglass shape under their abdomen.

Black widow spider

Keep Out!

Since it is much more difficult to deal with fall invaders once they have gotten inside, take measures to exclude these pests before late autumn when they begin to seek overwintering sites. Repair holes in window and door screens, re-caulk around windows, doors, utility pipes and under wood fascia and replace any worn door sweeps. For pest prevention, consider early fall residual sprays applied to the outdoor foundation walls and other points of entry including door and window frames, around vents and where utility lines enter. Remember, prevention is the best defense!

From State-by-State Gardening September/October 2012. Photography by Douglas A. Spilker, Ph.D.


Posted: 11/21/12   RSS | Print


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