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Are Cat-Sized Rats Taking Over DC?

A recent mega-rat discovery is unsettling, but we probably don't need to worry too much.
Image via iStock.

Last week, Popville posted about a massive rat found in Columbia Heights. The headline said it all: “I will never sleep soundly again.” It echoed another incident from last summer when a different enormous rat (larger than the head of a shovel) was scooped off the sidewalk on a sunny day near U street. Could Washington’s rat population be getting…bigger?

Good news! That probably isn’t happening. “There’s no scientific evidence coming from any place that they are in fact getting larger,” says Robert Corrigan, an urban rodentologist (yes, that’s a thing) who’s studied rats for 30 years.

So what accounts for these two mammoth rodents? Corrigan points to three possible explanations. When rats are frightened, they will often fluff out their fur to make themselves look bigger. Some rats have hair so long that they can appear to be twice as large as they actually are. “That’s their defensive posture,” says Corrigan. “They’re trying to scare their predators away.”

But these rats were dead, so fur fluffing can’t be the answer. Another possibility: When rats (or any animals) die, all of the gasses and fluids in the body begin to bloat. Especially when the carcass is exposed to the sun, the gasses blow up the body and the softened decomposing skin begins to stretch. So a dead rat can often appear much bigger than it was back when it was scampering around the alley.

But the rat in the Popville pic didn’t seem particularly decomposed. Which brings us to the third option. While typical rats in DC weigh about one pound, there are other rat breeds that can get much bigger. Sometimes exotic breeds are imported as pets, especially something called a Gambian pouched rat, which is native to Africa and can weigh up to nine pounds, according to Corrigan. “People are bringing them in on the black market, like little puppies,” he says. “When they get too big they start biting and people release them.” These animals look basically identical to the common city rat, except they’re much bigger.

So we showed Corrigan the photo, and he confirmed that it was a Gambian pouched rat. Mystery solved. Fortunately, these monsters are unlikely to breed with the common city rat, so there’s no reason to worry about mutt-rats.

So no, this disturbing photo is not evidence that DC’s rats are suddenly getting bigger.

On the other hand, rats here could be slowly getting bigger. We just don’t know–nobody has bothered to measure. “Technically the answer to your question is that they could be getting larger in small increments,” says Corrigan. “But someone would have to formally scientifically test that. Is it possible it has changed in size? Yes. Is there any great [influx of] super rats showing up in this city? The answer is no.”

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