They may be scurrying near you.
A species of cockroach that can survive a freeze has been found for the first time in the United States in one of Manhattan's most popular parks, the West Side's High Line, according to a study published in the January Journal of Economic Entomology.
The Periplaneta japonica was discovered last year by an exterminator working at the park, who saw the bugs looked different, researchers from Rutgers and the University of Florida reported. They were found in mulch, rodent bait stations, sprinkler control boxes and under the boardwalk, the study said.
"We really don't know what they're going to do," author Jessica Ware, a Rutgers associate professor and entomologist, said in an interview, "but they're definitely winter ready."
The roaches, identified by DNA tests, may become one of this region's most successful immigrants, the authors warned.
Unlike the roaches hated by most, Periplaneta japonica don't mind being out in the cold. The species originated in Japan's chilly, northern climes and has invaded Korea and China.
"This might increase the potential of this species to have a successful invasion, as they may be able to withstand the frigid winters," the authors wrote.
Japanese researchers once buried these cockroaches in ice for three hours to test their hardiness. When freed, the roaches took 10 minutes to recover in 77-degree weather, and the colder it was, the faster the recovery time, the Japanese scientists wrote. The roaches could even move on ice, they said.
Ware and the study's co-authors, graduate student Dominic Evangelista and insect identification expert Lyle Buss of the University of Florida, suspect the roaches arrived with imported plants lining the park. They said U.S. nurseries often carry imported plants.
"It's only been found in one location, and we don't really know if that means it's isolated to that location or whether it's already everywhere," she said.
Thomas Smarr, horticulture director for Friends of the High Line, said the situation is being monitored: "Fortunately, we do not believe this insect is having a negative impact on the park."
He said the plants come from U.S. nurseries, which are routinely inspected by federal regulators, and no issues were reported to park officials.
"The study speculated the source of the insect's arrival," Smarr said, "but we understand it did not check other parks, natural spaces and buildings nearby, so it's truly anyone's guess."
The rusty-brown roaches can be an inch long.
The likelihood that all these varieties can interbreed and result in a "hybrid super-roach" is slim due to their sexual incompatibility, experts said.
It's possible roach numbers will fall as newcomers and their cousins spend so much energy competing for food that they have less time to breed, she said.But still, an explosion in this hardy species' numbers could call for new extermination methods, Ware said. Spray inside and Periplaneta japonica can go outside, moving back in when the killing cloud dissipates, she said.
Researchers may want to see what parasites and pathogens are carried by these insects, Ware said, and whether these roaches also cause allergic reactions in some humans.
For now, most folks won't feel a big impact, except to wonder whether it's the American or the Asian roach in the cereal box -- an entomologist ha-ha, Ware said, joking. The Manhattan discovery has thrilled insect biologists. They can be "cockroach detectives," using regional genetic differences in the species to see where the High Line group has been and when it arrived.
"We definitely don't like invasive species coming into an area," Ware said. "But it is exciting to have another cockroach to examine."