pest-control

Boxelder Bugs and Asian Lady Beetles: Minnesota's Fall Invaders

Boxelder bugs and Asian lady beetles swarm Minnesota homes every fall. Learn how to spot them, seal them out, and handle the ones that surface in winter.

Boxelder Bugs and Asian Lady Beetles: Minnesota's Fall Invaders

On a warm afternoon in early October, walk around to the south side of almost any house in Minnesota and look at the siding. There is a good chance you will find it crawling with black and red bugs, orange beetles, or both, all soaking up the last real sun of the year.

Those are boxelder bugs and Asian lady beetles, and they are looking for a place to spend the winter. Your wall voids, attic, and window frames fit the bill. They will not eat your house or your food, but a few hundred of them wandering across the living room ceiling in February is its own kind of problem.

Here is how to tell them apart, why they pick certain homes, and what you can still do this fall to keep most of them outside.

How to Tell Them Apart

Both insects show up at the same time and on the same walls, so people often lump them together. They behave a little differently, though, and knowing which one you have helps you decide what to do.

Boxelder bugs are true bugs, not beetles. Lady beetles are the same family as the ladybugs in the garden, which is why they surprise people when they turn into a nuisance.

Boxelder bugs

Adults are about half an inch long, flat, and mostly black with red or orange lines along the edges of the back and wings. The young ones, called nymphs, are smaller and bright red, and you often see both together in late summer.

They feed mainly on the seeds of boxelder trees, along with maple and ash seeds. A yard with a seed-bearing female boxelder nearby tends to host a lot more of them, though they can fly in from several blocks away.

Asian lady beetles

These are rounder, about a quarter inch long, and range from pale yellow to deep orange or red. The spot count varies a lot, and some have no spots at all. The easiest tell is a black mark shaped like an M or a W on the white area just behind the head.

Native Minnesota lady beetles mostly spend the winter outdoors in leaf litter. The Asian species prefers cliffs and rock faces in its home range, and a sunny, light-colored house wall looks like the next best thing.

Why Your South and West Walls Get Covered

Both insects gather on the warmest surfaces they can find as the nights turn cold. In Minnesota that means south and west facing walls in September and October, especially on bright afternoons after a chilly morning.

Lady beetles tend to swarm on the first warm days after a hard frost. You might see almost none for weeks, then thousands on a 65 degree afternoon in mid October. Boxelder bugs build up more gradually, starting in late summer and peaking as the weather turns.

Light-colored siding, houses standing alone near woods or fields, and homes with lots of sun exposure draw the biggest crowds. Once they land, they crawl into any gap they can find: under siding laps, behind window trim, around soffits, and through vents.

Are They Doing Any Damage?

Neither insect harms wood, wiring, insulation, or the structure of your house. They do not breed indoors, they do not eat stored food, and boxelder bugs do not bite.

The trouble is the mess. Crushed boxelder bugs leave a reddish orange smear that can stain light carpets, drapes, and painted walls. Asian lady beetles release a yellow fluid from their leg joints when they feel threatened, and it stains fabric and smells bitter and musty.

Lady beetles can also give a small pinch when they land on skin. It rarely breaks the skin, but it catches people off guard. Some people also report allergy symptoms when large numbers die off inside wall voids or window frames.

If a boxelder bug does get crushed on fabric, blot it with cold water and a little dish soap right away rather than rubbing. Lady beetle stains respond the same way. Heat from a dryer or an iron can set both for good, so treat the spot before it goes in the wash.

Seal the House Before It Gets Cold

Exclusion is the most effective fix, and much of it is DIY work. The goal is to close the openings bugs use to get from the siding into the walls and living space.

Walk the south and west sides first, since that is where most of them gather. Look for gaps around window and door frames, where siding meets the foundation, around outdoor faucets and cable lines, and at the soffit and fascia.

A few tubes of good exterior caulk, a can of expanding foam for bigger holes, and fresh door sweeps usually cost well under $100. Check that window screens fit tight, and make sure attic and dryer vents have intact screening. Caulking on a cold day is harder, so this work goes best on a mild afternoon in September or early October.

When a Perimeter Treatment Makes Sense

An exterior insecticide application can help if it goes on at the right time. It works best in late August through mid September, before the big aggregations show up, and it goes on the sunny sides of the house where they land.

Once the bugs are already inside the walls, spraying does very little. Treating indoors is not recommended in most cases, since dead insects in the wall voids can draw carpet beetles and other scavengers later.

If you hire someone in October, ask what they will treat and why. A good tech will focus on sealing and targeted exterior work rather than spraying rooms inside the house.

Vacuum Them, Don't Squash Them

For the bugs that make it inside, the vacuum is your best tool. Squashing boxelder bugs or lady beetles leaves stains and odor, and sweeping them up with a broom does much the same.

A shop vac works well. So does an old nylon stocking pushed into the end of a regular vacuum hose and held in place with a rubber band, which lets you dump the bugs outdoors without filling the vacuum bag with the smell.

Some homeowners set up simple light traps in attics or unused rooms. They help a little, but the vacuum does most of the work.

Empty the stocking or shop vac outside, well away from the house, and on a cold day if you can. Bugs dumped into a warm flower bed next to the foundation will often just crawl right back up the siding.

What to Expect Once Winter Sets In

Most of the insects that got into your walls in October will sit quietly through the coldest months. The surprise comes on sunny days in January, February, and March, when the sun warms a south wall and fools them into thinking spring has arrived.

They crawl out toward light and warmth, so you find them on windowsills, lampshades, and ceilings near exterior walls. They move slowly, they cannot get back outside, and many die on the sills within a few days.

This is normal and does not mean you have an infestation that is growing. Keep vacuuming, keep notes on where they appear, and use that list to guide next year's sealing.

Twin Cities, Duluth, Rochester, and St. Cloud

The timing shifts a bit depending on where you live. In the Twin Cities metro, aggregations often peak in late September through mid October, with lady beetle swarms on the first warm days after frost.

Duluth, MN tends to run earlier because of cooler nights near Lake Superior. Homes on the hillside with big sunny southern exposures can get hit hard, and the swarm window sometimes closes by early October.

Rochester, MN usually sees the southern Minnesota pattern, with farm fields and wooded edges feeding large lady beetle numbers in October. St. Cloud, MN often falls in between, with boxelder activity strong along the river where boxelder trees are common.

What Professional Help Costs

Most homeowners handle these insects on their own, but hiring help makes sense for tall homes, heavy infestations, or anyone who does not want to be on a ladder. Prices below are rough ranges and vary by company and house size.

A single exterior perimeter treatment typically runs about $150 to $350. Professional exclusion work, including sealing gaps, screening vents, and caulking around trim, often costs $300 to $1,000 or more depending on the size of the house and how much of it needs work. Seasonal packages that combine a late summer treatment with a fall follow-up usually fall around $250 to $500.

Some general pest plans include occasional invaders like these at no extra charge. If you are already on a quarterly plan, ask before paying for a separate visit. You can compare local providers through our list of pest control companies near you, and more seasonal home guides are on our home maintenance blog.

Fall Invader Questions

Should I cut down my boxelder tree?

Usually not. Removing one tree rarely solves the problem, since boxelder bugs fly in from surrounding yards, and a large tree removal can cost $800 to $2,000 or more. Sealing the house does far more for the money.

Do Asian lady beetles bite people?

They can give a small pinch, especially when they land on skin in large numbers. It rarely breaks the skin and is not dangerous, though the yellow fluid they release can stain clothing.

Why are bugs showing up in my house in February?

Insects that got into the walls in fall wake up when the sun warms the exterior. They wander toward windows and lights, cannot survive long indoors, and a vacuum handles them.

Can I spray them inside?

It is not a good idea. Indoor sprays kill only the few you can reach, and dead insects in the walls can attract carpet beetles, so seal from the outside and vacuum the rest.