Stink bugs invading Michigan homes: Why invasive pest come inside and what controls them

(FOX 2) - Temperatures are falling, daylight is disappearing, and stink bugs are responding.

Homeowners beware: the seasonal changes mean these little invasive monsters will be looking for somewhere to stay warm over the winter and one of their favorite places to hunker down is inside one's home.

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The brown marmorated stink bug is not native to Michigan. That has left it to spread without much resistance through the state, wreaking havoc on crops and invading households. 

"They are looking for shelter. Even though the weather is beautiful, they realize that and are looking for winter shelter," said Mariana Szucs. "People's homes are perfect for that."

Szucs studies the invasive stink bug at Michigan State University. She said now is about time the critters start showing up inside people's homes.  

"They'll look for any crevices on homes or windows. Sometimes they go under the siding on homes," she said. "That's one way to overwinter. Other ways would be under tree bark or in wood sheds."

The invasive stink bug

While some stink bugs are native to Michigan, a particular variant from east Asian called the brown marmorated stink bug is what researchers are most concerned about.

They can be identified by the shield shape of their body, ranging between 14 and 17 mm long. They're about the size of a dime and are colored with a brownish hue. 

Females typically lay 20-30 light-green eggs on the underside of leaves.

By the time it first appeared in Michigan in 2010, it had already established other states further south. 

The invasive bug is a major pest to agriculture, feeding on numerous fruit and vegetable plants, ranging from apricots, peas, cherries, corn, grapes, peaches, peppers, and tomatoes.

In Michigan, they're a particular problem because of the state's apple trees. Invasive stink bugs feed on both the fruit and its leaves. 

The pest is hard to control because of the stilts it has on its feet. This enables them to avoid the pesticides that farmers might spray on crops to keep them away. 

Why you should care:

It's also a problem for homeowners who can expect to see them appear inside their homes when fall arrives. The adults recognize this shift and will head for any shelter to keep them away from harsh temperatures. 

This year could see a bit of a delay in their shift indoors. But that could mean even more will come inside once their behavior changes. That's because only adults seek shelter. Their young cannot fly and, until they develop wings, won't be able to go indoors.

"What I think is happening is, it's been an unusually warm fall, which will allow the nymphs to develop, so there will be more of them going into the house," she said. "It's been a good year for them."

It's only anecdotal, she admits, but invasive stink bugs have thrived in warm conditions and could find success as average temperatures continue to trend upwards.

Parasitic Samurai Wasp

While farmers have struggled to control the species and prevent their crops from being impacted, Michigan does have one thing going for it: the brown marmorated stink bug's native predator is also in the state.

The samurai wasp is a parasite exclusively tuned to feeding on stink bug eggs. Smaller than one's finger nail, a female will seek out stink bug eggs and lays its own fertilized egg inside the shell. Weeks later, a wasp will emerge, eating its way through the casing.

While specialists like Szucs have studied introducing the wasp to keep stink bug numbers down - a process called biological control - they weren't behind the insect's introduction in Michigan in 2018; it arrived on its own.

It may take years for it to establish, but where stink bugs go, the wasp is expected to follow.

What homeowners can do

The best thing people can do to keep stink bugs from getting in their homes is by sealing up the spaces where the invasive pests are climbing through.

That means caulking windows, fixing holes, and sealing gaps in the siding.

If they do get inside, the one thing someone should not do is squish the bug. Doing so releases an odor that's designed to keep away predators, but also smells to people as well.

Peppermint spray also works as a natural deterrent for pests. Administering it to sections of a home where they get inside can keep them away.