The pea-sized bugs look a bit like ticks, can suck one-fifth of the yield out of a soybean field, and travel by highway.

In the 5 1/2 years since they were first spotted in Georgia, kudzu bugs have spread 400 to 500 miles west and north as far as Louisiana, Arkansas, Washington, D.C., and its suburbs, and southern Delaware.



``We don't know any way to stop it,'' said Blake Layton, a Mississippi State University entomologist.



Kudzu bugs range from green to a brown so dark it's almost black. They look a bit like ticks and a bit like dark ladybugs with squareish backsides. Like their cousins the stinkbugs, they stink. Some people say the smell is fruitier than stinkbugs' stench; others say it's far more pungent.



Ultimately, cold winters and lack of kudzu probably will decide just how far kudzu bugs spread, said Wayne Gardner, an entomology professor at the University of Georgia.



Their favorite food is kudzu, but they can also get through Southern winters on soybean plants, Gardner said. ``But then you've got to factor in temperature. In Minnesota or the Midwest, I'm not sure the bugs are going to survive,'' he said.



They've spread far and fast by hitching rides. They're attracted to light colors, especially white. If a white truck, RV or car stops near a soybean field or kudzu patch, it is likely to carry at least a few, which will alight at any stop near their favored plants or wisteria, another Asian import.



It only takes one. Every kudzu bug in the country carries the genes of a single female that apparently traveled from Asia by air, since the first sighting was not far from Atlanta's Hartsfield-Jackson International Airport.



Gardner said last year's cold winter and spring seem to have slowed the spread.



About 30 counties reported their first infestations last year _ about one-quarter the number that did so in 2013, according to a map of the insect's spread since the summer of 2009. Last year's new locations included 15 Mississippi counties and nine in Louisiana, with Virginia, Florida, Arkansas, Alabama, and Kentucky each reporting one or two.



So far this winter, Gardner said, there hasn't been enough prolonged cold to slow them again.



The bugs tolerate cold better than fire ants, which aren't much of a problem north of the Mason-Dixon Line, noted John Coccaro, an Agricultural Extension Service agent in Warren County, where they were first sighted in Mississippi.



He said his office in Vicksburg gets flooded in the fall by calls about kudzu bug home invasions.



``If you swat at them they stink and make a mess, stain your furniture,'' he said.



Though eradication may be impossible, kudzu bugs can be controlled, entomologists say. They've done less damage than stinkbugs to Louisiana's soybeans and can be killed by the same pesticides, said Sebe Brown, an assistant area agent for the LSU AgCenter in north Louisiana.



As with ladybugs, any that get indoors should be vacuumed up, Coccaro said.



To keep them out, homeowners can caulk cracks, make sure screens don't have holes and take other steps used to keep ladybugs and mosquitoes outside.



Gardner said kudzu bugs aren't as big an indoor problem as ladybugs.



``These things generally don't like to go into dark places. They don't seem to overwinter in attics like ladybeetles do,'' he said.

