Tehran has a rodent problem. A big one. Rats not only easily outnumber the city's residents (an estimated 25 million versus 12 million, respectively), they're monstrously large. According to NPR, these vermin can weigh up to 11 pounds—more than some cats.
The city has always had a problem with rats; every spring, the water from snow melting off the Alborz mountains flushes the rats out of their underground lairs. Way back in 2000, NPR noted, the BBC reported that poisoning the rats, which makes them thirsty and forces them underground as they search for water, didn't work. If anything, it seemed to make the rats stronger.
An environmental adviser to the city council, Ismail Kahram, told the website Qudsonline.ir, "They are bigger now and look different. These are changes that normally take millions of years of evolution."
So now, in addition to chemicals, officials have deployed sniper teams equipped with infrared lights for nighttime hunting. So far, the teams have succeeded in taking down only some 2,000 of them.
"It's become a 24/7 war," Hadi Heydarzadeh, the head of Tehran municipality's environmental agency, said last month. "We use chemical poisons to kill the rats during the day and the snipers at night."