Uninvited Fall Guests

Insects and other arthropods intersect our lives daily. When they make their way into homes in fall, they are most often uninvited. Fall home invasions are nothing out of the ordinary for insects; they are just seeking shelter and protection from winter. Wall voids and interior walls provide optimal temperatures for residing. Knowledge of these insects and their behavior can help to reduce fear and unnecessary pesticide use within the home.

Some of the common invaders include seed bugs (western conifer seed bugs, boxelder bugs, and tuxedo bugs), false chinch bugs, root weevils (crusted root weevils, strawberry root weevils, and black vine weevils), cluster flies, spiders, and millipedes. Insects are frequently added to the list each year with new establishments and changes in behavior and climate. Any small opening around the house can provide access for an insect, including holes in screens, underneath doors, and small cracks in the foundation. Many insects bask in the sun on south- and west-facing walls of buildings in late summer and early fall.

Our common fall home invaders are mostly harmless to humans and pets and do not transmit diseases. Spiders can bite but typically only bite if threatened or if trapped in clothing, shoes, etc. After these home invaders enter the house, most eventually enter a semi-dormant state. Some might emerge on warm, winter days, but most do not survive the winter inside the home. Some spiders can potentially stay longer. Their presence in the house does not necessarily indicate that they are harming nearby plants in the yard.

Western Conifer Seed Bugs (A)
Western conifer seed bugs feed on the seeds of pine and Douglas-fir trees. They are often mistaken for the kissing bug species (assassin bugs) that can vector Chagas disease, which we don’t have in Montana.

Boxelder Bugs (B)
Boxelder bugs occur every fall. Sometimes it is baffling why they are around without boxelder trees in the yard, but they also feed on the seeds of maples, ash, and several fruit trees. They can stain lighter fabrics if smashed.

Tuxedo Bugs (C)
Tuxedo bugs are one of our newest guests, and hundreds of these insects can be present at a time. They feed on plants in the mint and figwort families (like white mullein) and seem to prefer buildings adjacent to weedy areas or abandoned lots.

False Chinch Bugs (D)
False chinch bugs enter buildings in search of moisture and humidity. When not aggregating on buildings, they are sap-feeding insects and feed on weeds such as flixweed, plants in the mustard family, turf, kochia, and pigweed. Aggregations can be in the hundreds.

Root Weevils (E–H)
We have several different species of root weevils, ranging in size from one-sixteenth to one-quarter inch. As their name implies, the immature weevils feed on the roots of several ornamental plants. Fortunately, the damage is minimal. As adults, they chew small notches on the outside edges of leaves.

Cluster Flies (I)
Cluster flies look like a larger house fly. There can be hundreds of flies congregating on the sunny sides of buildings in late fall and entering through attics and higher areas. Unlike most flies, they do not breed in decaying organic matter. Rather, they are parasites of earthworms.

Spiders
During late summer and early fall, it is normal for spiders to enter buildings and homes. This includes hobo spiders which are prevalent in Montana basements, lower levels of buildings, and window wells from August through November. Common misunderstandings about the hobo spider have caused unnecessary concern. There is no conclusive evidence that the hobo spider is harmful to humans.

Garden Millipedes
Millipedes feed on decaying plant material. They can mass migrate into buildings following wet weather events in the fall but will only survive for a day or two inside the home without moisture.

Preventing Home Invaders
It is best to make the house inhospitable on the outside before fall, especially south- and west-facing areas. The following tips can help to keep insects from entering the house:

• Install door sweeps at the base of exterior doors.
• Seal all cracks in the siding.
• One point of entry is the meeting of the foundation and siding of a building. Caulk or fill this juncture.
• Seal utility openings where pipes and wires enter the foundation or siding.
• Avoid storing firewood next to and inside the house. Many home invaders like to rest in firewood piles.
• As a last resort, chemical treatments can be used in the form of barrier sprays in late summer/early fall to kill insects on the outside of the building.
• The base of doors and windows should be treated.
• Apply materials to a two- to six-foot-wide band along the soil around the foundation and two to three feet up the foundation walls.
• Pyrethroid insecticides (active ingredients permethrin, bifenthrin, deltamethrin, cypermethrin, lambda-cyhalothrin, esfenvalerate or cyfluthrin) are preferred because they are effective at low temperatures. Always read and follow the product label to ensure you are using the correct pesticide product safely and effectively.

After they have already entered the home, use the vacuum to remove unwanted insects. Limit the use of insecticides inside the home. Very few are labeled for this use, and effective contact with the insect is challenging.