They came from China, Japan, Korea. They hid in containers full of trade goods and silently entered the United States.

There was no warning.

At first, they conquered the East Coast. Last July, a relative was spotted near Champaign, in the South Farms.

This spring, they are in full invasion mode in East Central Illinois.

If you find one, you can squash it. But there will be a cost: a horrible stink that gives this bug its very name.

The brown marmorated stink bug is one of hundreds of similar insects.

Michael Gray, a professor in the Crop Sciences Department, said these stink bugs are a real concern because they're dangerous to crops, and breeding rapidly westward.

"They began moving westward from Pennsylvania, first sighted around Allentown, and they keep coming on," he said.

"They're a threat to bean fields, and they are likely to cause home-owners' headaches because they try to get into their homes to overwinter," Gray said.

But don't crush that bug.

Like the also-stinky lady beetle, there's a better way than squishing to get rid of it in your household: the vacuum cleaner, says University of Illinois Extension entomologist Phil Nixon.

But on acre after acre of soybeans, no farmer has a vacuum cleaner quite that big, and young soybean pods are very vulnerable, having also originated in Asia.

For homeowners, it's tomatoes at risk. Even more vulnerable, Nixon says, are soft fruits like peaches and cherries.

Brown marmorated stink bugs are not the first of their kind to make an insidious entrance.

Ever vigilant, UI teaching associate Patricia Stoller first spotted an invading stink bug last July.

She teaches Introduction to Crop Sciences and was looking at a pest newsletter from Kentucky about the bugs coming up from Mississippi and threatening bean crops.

She looked at the photo, then looked at an insect in South Farms.

"It was like looking at the missing child on a milk carton and recognizing" the missing child, she said.

She took a photo, but didn't take the actual bug, so she's not sure whether it was a red-banded or red-shouldered stink bug, which you can only tell by looking at the underside.

"They're both a soybean issue," Stoller noted.

Gray said the stink bugs are especially threatening because "these are pretty good size, about the size of a thumbnail, and they have a large host range."

And most of all, they are voracious.

"They have needle-like piercing, sucking mouth parts. They feed on a variety of fruits and vegetables," Gray said.

Asian-originated soybeans are a natural feast, but good old American corn is also endangered, particularly while young.

"They have the ability to feed on soybean pods, but they can feed on corn as well. They injure developing kernels with their mouth parts," Gray said.

He said entomologists are ready to fight back.

"This year, we're going to conduct a statewide survey, at least within soybeans. Over time, populations will begin to build and more firmly entrench themselves if we don't fight back," Gray said.

The surveys in the field are sponsored by the Illinois Soybean Association.

Soybean farmers on the East Coast have had some success using pyrethroid insecticides in their fields to protect developing plants.

Gray is wary of using insecticides in the home, though.

The first step against stink bugs in the home involves vigilance and elbow grease. When they're trying to get into the house from outside, insecticide or just soapy water is effective.

Once inside, it's you versus them.

"I've seen pictures from the East of people using brooms and dust pans to get rid of them," he said. "I recommend a vacuum cleaner."

Insecticides within the home are a bad choice, Gray said, because outside, sunlight and rainwater degrade them. Inside, they can linger for a long time.