Illustration: Rebecca Zisser/Axios

One not-fun consequence of booming cities is the scourge of rats, well fed by trash, warmed by climate change, and bringing new health threats and general grossness with them.

The big picture: “Everywhere I go, rat populations are up,” scientist Robert Corrigan tells the NYT.

  • He estimates that rat numbers may be up 15–25% in some municipalities, including Philadelphia, Los Angeles, New York City and Washington, D.C.

By the (horrifying) numbers, courtesy of National Geographic:

  • "[A] litter of nine pups 10 weeks into the year would grow to 270 pups by the 30th week and wrap up with a whopping 11,907 rats by year’s end."
  • "Rats usually reach sexual maturity by 12 weeks, and litters can vary from two to 14 pups."
  • "Reproductive rates are highly dependent on environment. The more shelter, food, and trash, the higher the rat count."

What's next: Cities are trying lots of things to fix their rat problems, and they're mostly failing.

  • Poisoning and suffocation (via dry ice) has mostly failed. Survivors can rapidly repopulate an area.
  • D.C. has even tried sterilizing the little devils.
  • On the other coast: "Rat-infested piles of rotting garbage left uncollected by the city of Los Angeles, even after promises to clean it up, are fueling concerns about a new epidemic after last year's record number of flea-borne typhus cases." (NBC 4 LA)

The bottom line: "Until cities radically change how they deal with their trash, Corrigan says, 'the rats are winning this war.'"

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