Gambian pouched rats have re-emerged in the Florida Keys after a two-year hiatus, renewing fears they could spread deeper into a state already beset by invasive species. Native to central and southern Africa, the muroid rodents grow larger than cats, can weigh up to 9 pounds, and have a history of spreading monkey pox.

The Florida outbreak originally began sometime around 2001, according to the Florida Fish and Wildlife Conservation Commission, when a breeder who raised the rats as pets released six or seven on Grassy Key. (They were often imported to the U.S. as exotic pets before 2003, when they were banned after being linked to a monkey pox outbreak. The Food and Drug Administration later lifted that ban in 2008.)

Gambian pouched rats can have five litters every nine months, with each litter averaging four offspring, according to the FWC. And since they become sexually mature about five months after birth, it didn't take long for those six or seven colonists to establish a local breeding population.

Conservationists soon grew concerned the invasive rats might spread to the Florida mainland, where they could wreak havoc in fragile ecosystems like the Everglades, which is already dealing with several other exotic pests. Federal and state officials began a poisoning campaign on Grassy Key in 2007, laying out peanut-butter bait laced with toxic zinc phosphide. As FWC exotic-species coordinator Scott Hardin tells the Florida Keys KeyNoter, the traps initially seemed to work.

"We thought we had them whipped as of 2009," Hardin says. "[But] in the early part of 2011, a resident emailed me and said he saw one of the rats. We were skeptical but went back and talked to people and [saw] there were rats that we missed."

Officials have caught about 20 of the rats since then, Hardin adds, all within a half-mile of each other. "We think they have not moved far but they clearly reproduced. We are surveying the area and have been taking pictures of rats ever since," he says.

As wildlife biologist Gary Witmer from the U.S. Department of Agriculture told Reuters in 2007, Gambian pouched rats "sure can bite," and "we're lucky" none in Florida have showed signs of monkey pox. They may also compete with native Key Largo wood rats, which are endangered, and they're known to damage food crops in their native Africa. A recent USDA report warns that "if this species reaches the mainland, there could be extensive damage to the Florida fruit industry and other agricultural commodities. ... A climate/habitat modeling exercise suggested that their new range in North America could expand dramatically if they reach the mainland."

Another round of trapping is planned for later this summer, Hardin tells the KeyNoter, and will likely continue for at least five months — or "until we see signs that we have knocked them back." If that doesn't work, there may still be another deterrent that keeps the rats from colonizing Florida, albeit an imperfect one: the estimated tens of thousands of alien pythons that have already infiltrated the Everglades.

If you're in South Florida and think you see a Gambian pouched rat, you can report it using this form, or by calling Florida's invasive species hotline at 1-888-IVEGOT1.

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[Via Florida Keys KeyNoter]

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.

Cat-sized rats reappear in Florida Keys
Giant Gambian pouched rats are once again scurrying around the Keys, years after wildlife officials thought they had wiped out the invasive pests.