Occasional Invaders: Seasonal Pests in Your Home
Some pests only enter homes under specific conditions. These occasional invaders are not permanent indoor residents and typically live outside. However, when outdoor conditions become too wet, dry, hot, or cold, they seek shelter indoors.
Types of Occasional Invaders
Occasional invaders can be categorized into two groups:
1. Perimeter Invaders
These pests live around a building’s foundation in mulch, woodpiles, and plants. They enter homes when environmental conditions change. Examples include:
- Earwigs
- Sow bugs & pill bugs
- Millipedes
- Clover mites
- Springtails
- Crickets
Since they are not adapted to indoor conditions, most die quickly once inside.
2. Fall Invaders (Overwintering Pests)
These pests enter homes in the fall to escape the cold. Many overwinter outdoors under tree bark, mulch, or stones. However, if a warm building is nearby, they take advantage of gaps and crevices to move inside.
Common fall invaders include:
- Asian lady beetles
- Brown marmorated stink bugs
- Cluster flies
- Elm leaf beetles
- Boxelder bugs
- Kudzu bugs
- Western conifer seed bugs
How Fall Invaders Enter Homes
Most overwintering pests do not intend to live indoors but rather seek shelter. Many stay hidden outside under siding, shutters, or roof eaves. However, they may find entry points through:
- Cracks in walls or siding
- Gaps around windows and doors
- Vents and chimneys
- Unsealed utility openings
Once inside, they hide in attics, wall voids, baseboards, and carpets. When temperatures rise in spring (or during warm winter days), they become active again, often appearing on walls and windows as they try to exit.
Why Some Homes Have More Fall Invaders
Fall-invading pests are more common in homes near fields, orchards, or wooded areas. Since many overwintering pests feed on crops or trees, properties close to these habitats are at higher risk of infestations.
Additionally, certain species—like the brown marmorated stink bug—are expanding into new regions, making some areas more prone to new pest problems.
How to Prevent Fall and Occasional Invaders
The best time to control fall-invading pests is before they move inside. Prevention includes:
- Perimeter Treatments – Applying pest control barriers around the home’s foundation in late summer or early fall.
- Pest-Proofing the Home – Sealing cracks, gaps, and openings where pests may enter.
- Removing Attractants – Keeping mulch, woodpiles, and dense vegetation away from the foundation.
- Treating Host Plants – Managing outdoor plants that attract these pests.
Identifying Common Fall Invaders
Here are some of the most common overwintering pests and their characteristics:
1. Asian Lady Beetle (Harmonia axyridis)
- Location: Found throughout the U.S. and Canada
- Size: 1/4-3/8 inch (6-10 mm)
- Color: Yellow to dark reddish-orange with black spots and an “M” shape on the thorax
- Behavior: Predator of plant-feeding insects but a nuisance indoors
2. Boxelder Bug (Boisea trivittata)
- Location: Found across the U.S. and Canada
- Size: 1/2 inch (11-14 mm)
- Color: Black with red-orange markings along sides and wings
- Behavior: Feeds on female boxelder and silver maple trees
3. Cluster Fly (Pollenia rudis)
- Location: Found in most of the U.S. and Canada, except Gulf states
- Size: 3/8 inch (8 mm)
- Color: Dull dark gray with golden hairs on the body
- Behavior: Larvae parasitize earthworms; adults enter homes in large numbers
4. Brown Marmorated Stink Bug (Halyomorpha halys)
- Location: Found in 41 U.S. states and two Canadian provinces
- Size: 1/2-5/8 inch (12-17 mm)
- Color: Mottled brown-gray with white-banded antennae
- Behavior: Feeds on fruit trees and crops; releases a foul odor when disturbed
5. Kudzu Bug (Megacopta cribraria)
- Location: Found in southeastern U.S. states
- Size: 1/8-1/4 inch (4-6 mm)
- Color: Shiny olive-green with brown speckles
- Behavior: Feeds on kudzu and soybean plants
6. Elm Leaf Beetle (Xanthogaleruca luteola)
- Location: Found throughout the U.S.
- Size: 3/16-1/4 inch (5-7 mm)
- Color: Yellow to olive-green with black stripes and spots
- Behavior: Feeds on elm trees, especially Siberian elms
7. Western Conifer Seed Bug (Leptoglossus occidentalis)
- Location: Found across northern U.S. and Canada
- Size: 3/4 inch (16-20 mm)
- Color: Dull brown with leaf-like extensions on hind legs
- Behavior: Feeds on seeds and needles of conifer trees
Final Thoughts: Preventing and Controlling Occasional Invaders
To reduce fall invaders, act before they enter. Sealing entry points, applying perimeter treatments, and managing outdoor conditions can significantly reduce their presence. Once inside, they are difficult to eliminate, but vacuuming and light traps can help manage small numbers.
For professional pest control solutions, consider seasonal treatments to keep occasional invaders out before they become a problem.
