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Homeowners Can Evade Fall-Invading Insects

As the air starts to get nippy in September and October, some kinds of insects begin to look around for a nice place to call home for the winter. Unfortunately, they may choose your house.

A few bugs are an annoyance, but a full-scale insect invasion can be a serious problem, said Phil Pellitteri, University of Wisconsin-Extension”s “bug doctor.” Pellitteri has some tips for dealing with an infestation.

“Several kind of insects may swarm into a house in September and October, looking for a place to spend the winter rent-free.” said Pellitteri, a professor of Entomology at the UW-Madison College of Agricultural and Life Sciences. “Among the worst are cluster flies.”

Cluster flies look like ordinary houseflies. Around the middle of September, they start coming into homes – sometimes by the millions.

“These little stinkers climb under siding and crawl up into attics. I”ve seen them packed tightly under siding and stacked as deep as five or six inches in an attic,” Pellitteri said. They also head for chimneys — lighting an October fire in the fireplace may result in thousands of flies swarming into the house.

Pellitteri said cluster fly larvae are earthworm parasites, so they do well in moist years – when earthworms are plentiful. An invasion is most likely in a house that sits alone in an exposed area, especially if that house offers opportunities for the flies to enter. ”

“Old houses have lots of cracks and leaks, but even in new construction, flies can enter through holes in soffit or roof vents.

Pellitteri recommends screening and caulking any possible entry points for insects as the best line of defense. If the flies come, he says, it”s important to get rid of them quickly – after they are inside wall spaces it is almost impossible to get to them with insect sprays. The commercial spray most often used against cluster flies is called Pyrethroid, a spray that works in cooler temperatures when other insecticides lose effectiveness.

“Cluster flies are a double problem because when they die in a house, they become food for carpet beetles,” Pellitteri added.

Once you get those cluster flies under control, it”s time to watch out for another invader, the Asian lady beetle. Pellitteri said this multi-colored beetle starts looking for lodgings in mid-October.

This species was first recorded in Wisconsin in 1992, but it has quickly spread around the state. Outside, the beetles are beneficial because they feed on the aphids that munch garden vegetable and flowers. In the house, they are harmless, but they bleed orange if they are hurt.

“The best way to deal with lady beetles in the house is just to vacuum them up. But don”t use a vacuum with a beater bar. It will crush the beetles and stain carpets.” If lady beetles are swarming around the outside of the house, Pellitteri says homeowners should make sure cracks and openings are sealed. Some people may choose to spray the exterior walls to keep them from getting inside.

Box elder bugs — orange and black and about an inch long – live in box elder trees in the summer, but look for shelter in the fall. Houses with box e lder trees growing nearby are likely to be invaded.

“The only enemy of the box elder bug is a fungus disease, so they do well during long dry summers.” Pellitteri said. “They are quite a nuisance.” A soapy water spray directed at bugs massing on exterior walls would kill them, he added.

Another invader, the western pine leaffooted bug is chestnut brown and a little bigger than a box elder bug.

“This insect has moved into Wisconsin in the last eight to ten years” Pellitteri said. “If you disturb them, they give off a very strong piney smell. They don”t invade in large numbers, but people do get concerned about the smell.

For all these fall invaders, Pellitteri recommends physical barriers to keep them from entering houses and other buildings. And he said it”s important to act quickly when then an invasion begins because the bugs can be almost impossible to kill or remove once they”ve found a snug spot to spend the winter.