Boxelder Bugs in Iowa Homes

Updated 2026-10-21 · By Kasey, Waukee, Iowa

If your West Des Moines siding is covered in black-and-red bugs on a sunny fall afternoon, you are not alone. Homeowners in Waukee, Clive, Urbandale and across central Iowa see the same thing most autumns: boxelder bugs gathering on the warm side of the house and slipping inside for the winter.

Iowa State University (ISU) Extension calls the boxelder bug a common and well-known insect in Iowa. The good news is that it is a nuisance, not a danger. This guide explains how to identify boxelder bugs, why they show up when they do, what you can do yourself, and when it makes sense to bring in a licensed pest professional.

What it is and how to identify it

ISU Extension describes adult boxelder bugs as black and red and about 1/2 inch long. They often gather in clusters. The young bugs (nymphs) look bright red, because their black wings do not cover the abdomen until they become adults, so a mass of bugs on your foundation can include several sizes and shades.

Despite the name, boxelder bugs are not limited to boxelder trees. ISU says that during summer they live, feed and reproduce on trees, shrubs and other plants, including boxelder, maple, ash and others. ISU's 2019 fall invader update notes that two generations are produced during the summer on seed-producing boxelder and maple trees, as well as other flowers and shrubs.

Why they are a nuisance, not a threat:

• They are sap feeders. ISU says their beak can only suck liquid sap from twigs and seeds, and they do not cause significant damage to the plants they feed on.
• They do not reproduce indoors and do not feed indoors. They only lay eggs on trees and other plants.
• ISU states they are harmless and cannot damage the house, its furnishings or the people living in it. They can, however, be a considerable nuisance.

Not sure what you have? In the same season you may also see multicolored Asian lady beetles. ISU describes those as about 1/3 inch long, dome-shaped and yellowish-orange to red with variable black spots, with a black "W" shaped mark near the head. If you still cannot tell, the ISU Plant and Insect Diagnostic Clinic identifies insects for Iowans, including from photos. Check its website for current forms, options and fees.

Why it shows up (season and local angle)

ISU says boxelder bugs are most abundant after summers when May is very warm and July is very dry. Numbers vary a lot from place to place and year to year, so one West Des Moines street may be swarmed while a neighborhood in Waukee sees only a few. ISU adds there is no easy way to tell when and where there will be a problem until it starts.

In fall, boxelder bugs leave their host plants to find hiding places for the winter. During that search, ISU says they congregate in the sunshine on the south sides of buildings, trees and rocks. From there they get into houses through cracks in the foundation and siding, gaps along windows and doors, and other small openings.

Here is the part that surprises many Iowa homeowners. ISU explains that bugs inside walls or attics stay inactive while they are cold. The nuisance comes later, when bugs warmed by the furnace or the sun become active during the winter and crawl into rooms. ISU also notes that adults come out of hibernation in early spring. So a few bugs on a January windowsill are not breeding inside; they got in back in the fall.

What you can do yourself

Seal entry points first

ISU calls prevention the best deterrence: caulk and seal possible entry sites (cracks and gaps) before the bugs get in. ISU's fall invader articles add these pest-proofing steps:

• Make sure windows and doors fit tightly, and install tight-fitting door sweeps or thresholds.
• Replace damaged screens on windows and vents.
• Seal openings around pipes, wires and chimneys, and around the foundation.
• Caulk around windows, doors and other construction joints.
• Keep siding, eaves and soffits in good repair.

ISU is honest that the result will never be perfect, but every gap you close means fewer bugs in your living room this winter. The same sealing work also helps against fall mice, which we cover in our guide to mice in Iowa homes this fall.

Outdoor sprays: timing matters

ISU says spraying to reduce the number of bugs outdoors may limit the number that get into the house. Options ISU describes:

• Soapy water spray: ISU gives a recipe of 5 tablespoons of liquid detergent per gallon of water, sprayed directly on masses of bugs along the foundation in the fall. Repeated applications are usually necessary.
• A lawn and garden insecticide labeled for this use, applied to the bug masses or as a barrier.

Timing and placement tips from ISU:

• Treat the southern and western sides of the house, where the insects are most common.
• Insecticide barriers must go on before the bugs begin entering buildings to be effective. ISU gives September to mid-October as the window.
• Barrier products are short lived, can have non-target risks, and may need to be repeated during a long fall.

Always read and follow the pesticide label. The U.S. EPA notes that every pesticide label carries the statement that it is a violation of federal law to use the product in a manner inconsistent with its labeling. We do not recommend specific brands.

Skip the tree spraying

ISU says spraying trees in mid-summer has limited effectiveness, large trees are difficult to spray, and tree spraying is usually impractical. ISU's 2019 update adds that treating trees or gardens in summer is not effective in most cases, because insects can travel long distances from the surrounding area.

Bugs already inside

ISU is direct: there is no easy cure for boxelder bugs already in the house. They are generally not killed by household aerosol insecticides, and most residual insecticides are not of much benefit. ISU's sure method is simple: vacuum, sweep or pick them up and discard them as they appear. If you use an indoor product at all, ISU advises using insecticides indoors sparingly and following the label.

When to call a licensed pro

A professional can make sense when:

• Large numbers keep coming out of walls, attics or ceilings all winter, year after year.
• You cannot find or reach the entry points, such as gaps high on siding, soffits or around a chimney.
• You want an exterior treatment in fall but are not comfortable applying and reading the label for a barrier product yourself. ISU notes that additional insecticides are available to professional pest control operators for exterior fall treatment, and that professional treatment may be more effective than what homeowners can do with generally available household products.
• You have other pests at the same time, such as ants or wasps. See our Iowa ant guide and our wasp nest removal guide.

How to choose a licensed Iowa applicator

Under Iowa's administrative rules, anyone in the business of applying pesticides to another person's property must be licensed and certified by the state. Household pest work is Category 7A, General and Household Pest Control. Before you hire:

1. Ask for the company's Iowa license and the technician's certification.
2. Verify both in the Iowa Department of Agriculture and Land Stewardship lookup.
3. Ask whether the plan includes sealing entry points, not just spraying, and when they plan to treat.

See our guide to choosing a pest pro for more questions to ask.

Frequently asked questions

Are boxelder bugs harmful?

ISU Extension says boxelder bugs are harmless. They cannot damage the house, its furnishings or the people in it, and they do not reproduce or feed indoors. They are a nuisance, especially in large numbers.

Why do I see boxelder bugs inside in the middle of winter?

ISU explains that bugs that got into walls or attics in fall stay inactive while cold. When heat from the furnace or the sun warms them, they become active and crawl into rooms during the winter.

Is it too late to spray in late October?

For barrier treatments, often yes. ISU says insecticides must be applied before insects begin entering buildings, roughly September to mid-October. After that, focus on sealing gaps and vacuuming the bugs that appear.

Does soapy water kill boxelder bugs?

ISU lists a soapy water spray of 5 tablespoons of liquid detergent per gallon of water for bug masses on the foundation in fall. It works on the bugs it hits, and repeated applications are usually necessary.

Should I spray my trees in summer to prevent boxelder bugs?

ISU says tree spraying has limited effectiveness and is usually impractical, especially for large trees. Insects can also travel long distances from the surrounding area.