Accidental and Occasional Invaders

Accidental and Occasional Invaders

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Legends of the Fall
Accidental and Occasional Invaders

by Jody Green, Extension Educator

The pests in this article reflect some of the insects and arthropods most likely to invade Nebraska homes in the fall. Autumn is the time of year when days grow shorter, temperatures drop and the usual suspects begin the search for food and shelter. Many homeowners will discover these accidental and occasional invaders around the exterior perimeter this time of year.

Accidental Invaders: Nocturnal and Lost

Some arthropod pests enter structures accidentally. They are often attracted to light at night and wander inside by chance, through gaps under and around door thresholds and windows or through cracks in the foundation. Some homes are not the ideal habitat for accidental invaders. These pests do not lay eggs or complete their life cycle indoors.

When found indoors, they prefer locations that are cool, damp and dark such as basements, crawlspaces, garages, cold cellars, storage rooms and lower level bathrooms. Some may enter in large numbers, but do little damage; some may be sustained by feeding on insects or arthropods in the structure, but are generally considered nuisance pests.

Centipedes can be identified by their flat and elongated (1 to 1-1/2-inches long), reddish-brown, sometimes striped bodies. They have one pair of legs per segment and they move lightning fast! Two centipedes encountered indoors are the stone and house centipedes, which have 15 pairs of delicate, hair-like legs that fall off when handled (or smashed). Centipedes are not insects, but nocturnal predators of insects and use venom and their jaws to attack prey. They live outside in damp areas under leaves, boards, mulch in gardens and around foundations.

Millipedes can be identified by their cylindrical, elongated (1/16 to 1/2-inch long), gray-black, hard-covered, wormlike body. They have two pairs of legs per segment, move slow and tend to coil up when resting.

Pillbugs and Sowbugs are land crustaceans often called roly-polies. The difference between the two is pillbugs can roll into a tight ball when disturbed, but sowbugs cannot (due to two tail-like appendages).

Millipedes, pillbugs and sowbugs are all scavengers that feed on decaying organic matter of both plant and animal material. They have a high need for moisture and can be found outside in damp places hiding under rocks, boards, mulch, vegetation, grass clippings, trash and compost bins. They do not survive indoors for more than a few days unless there is a food supply and high moisture.

Crickets can be seen and heard around the structure at night. The field cricket has a black, robust body with jumping legs. Crickets prefer to live outdoors so they can feed on plant parts, but are known to get indoors and survive for up to two weeks. Field crickets do not breed indoors, but in large numbers can cause damage to fabrics and wall coverings, staining items with feces and vomitus.

Occasional Invaders: Looking for a Place to Overwinter

Some pests are considered occasional or seasonal pests and their grand entrance into your house in the fall may go unnoticed, but they are not accidental. Overwintering pests require a protective place to spend the adult stage of their life without freezing to death. They normally require a winter habitat between 40–50°F for hibernation. In the fall, large populations congregate on the warm, sunny side of structures, usually the southwestern facing exterior walls. Then they begin moving upward and find gaps leading inside. These pests do not lay eggs or multiply indoors, but will overwinter in wall voids, attics and unheated garages.

Most homeowners become aware of the infestation in the early spring when the sun warms up structures, stimulating a premature exit from their winter harborage. They are considered nuisance pests because of the sheer number of individuals that emerge and fly around inside trying to escape. They often come out from the ceiling through vents, lights, fans and other gaps, accumulating by the windows and leaving excrement and stains on walls.

Multicolored Asian Lady Beetles look like a native lady beetle but with a distinct black M-shape on their thorax before their wing covers. They can be many variations of color from a yellow to dark red, and have up to 19 black spots on their wing covers (or no spots at all). Multicolored Asian lady beetles are sometimes referred to as the Halloween beetle because they are seen congregating in late October. Outdoors they feed on aphids, mealy bugs, mites and other soft bodied plant pests — making them beneficial insects. Indoors when they emerge, they stain walls (reflex bleeding) when handled and have been known to bite — making them a nuisance pest.

Cluster flies are slightly larger than house flies, with yellow hairs on the thorax. They are attracted to the light-colored surface of structures and walk up looking for a gap to overwinter. They do not damage anything, but can leave dark fecal spots on windows and walls when they try to escape in the spring. When the adult cluster flies leave in the spring, females lay eggs in soil and their maggots are parasites of earthworms, using them as a food source.

Boxelder bug adults are 1/2-inch long, bright red or black, and have narrow reddish lines on their back. They are very common outdoors, active in all stages feeding on juices from the boxelder tree and sometimes maples. They are a nuisance pest in the fall when they gather on the building, but do little damage indoors until the spring when they emerge to lay eggs on boxelder trees. They have been known to produce an unpleasant odor when crushed and may puncture skin with mouthparts, if handled.

Pine seed bug is a dull reddish-brown with some patterns on its back and antennae almost as long as its body. It can be distinguished from the boxelder bug by its wide section of the lower hind leg. Outdoors they are found near evergreen trees feeding on the sap from green cones, twigs, seed pulp and sometimes pine needles. Indoors, they may release a terrible odor as a defensive mechanism, but are not known to damage property, hurt people or pets.


The most frightening group of fall invaders are spiders. Spiders are not insects, but arachnids. They have two body parts, eight legs, produce silk and contain venom. Some spiders create great anxiety and fear, but in the ecosystem they are considered beneficial predators. They prey on other accidental invaders, flies and silverfish to name a few. The spiders mentioned in this article are not aggressive nor harmful to humans and pets. Regardless of the species of spider, management for all spiders is similar to other invaders.

Wolf spiders are the largest based on the size of the body (1/4 to 1-1/3-inches long). Some are mistaken for a tarantula. They are medium to large body sizes, with long, hairy, sometimes patterned-legs and hairy jaws.

Wolf spiders can see in all directions with their eight eyes in this distinct arrangement: two largest eyes in the middle facing forward with two large eyes behind, and in front of those four, is a row of four smaller eyes. The appendages between legs and jaws are called pedipalps that help hold and manipulate the prey while feeding.

Many wolf spiders are nocturnal or active at dawn or dusk. They are active hunters and do not build webs to capture prey — some are patient ground hunters that patrol large areas while others build burrows in the ground. Female wolf spiders are known to provide unusual parental care by carrying around the silk egg sac until it hatches, and later carrying hundreds of baby spiderlings on her back after they emerge.

Funnel Weaver Spider are often mistaken for wolf spiders, but can be distinguished by the webs they build, which appear as a horizontal sheet with a small funnel-like tube off to the side or center. They are small to medium size (1/2 – 3/4-inch long) with tapered abdomen and prominent spinnerets at the rear. Legs are often banded, hairy and spiny. Funnel weavers have eight eyes of similar size arranged in two rows that curve toward the back of the body.

The funnel is used for protection and a place to hide. When prey lands on the web, the spider rushes out to catch it and drag it back into the funnel. The webs, which accumulate dirt and debris are found in the bushes, grass, flowerbeds, woodpiles, around windows, light fixtures and corners around the house. Occasionally webs are constructed indoors in dark corners of rooms and windows in basements and garages. Funnel weavers are nocturnal and disappear quickly when they see changes in light or shadows approaching the web. Males may be found wandering around searching for a mate, but females do not leave the web.

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