Although cities have ramped up their use of poisons and traps, the number of rats in places like New York City, San Francisco, and Toronto has increased in recent years, according to a new study published in the journal Science Advances. The researchers analyzed rat complaints and inspection reports for 16 cities that had consistent, long-term data available. More than two-thirds of those cities saw a significant increase in rat sightings.
“We are on our heels and being pushed backward,” Jonathan Richardson, the study’s lead author and an ecologist at the University of Richmond, says about the fight against rat infestations.
There’s more bad news: The study found a strong link between an increase in rats and rising temperatures, a consequence of climate change. Cities that had warmed more quickly had larger increases in rat sightings, the research found. This is in part because, with warmer winters, rats can spend more time eating and reproducing and less time hunkering down underground.
Scientists project that urban areas will warm by between 1.9 and 4.4 degrees Celsius (3.4 and 7.9 degrees Fahrenheit) by the end of the century, depending on how much oil and gas we burn. Cities tend to be hotter than rural areas—because concrete and other human infrastructure absorb and re-emit more heat than vegetation—and warm faster. That means that not only are current rat control methods failing, but the problem is likely to get much worse.
It’s a good thing, then, that there’s an obvious solution. And better yet, it’s simple. (...)
Part of the problem, experts say, is that for much of the past century, cities have relied on rodenticides and baited traps to eradicate rats.
This approach just doesn’t work.
“It’s fairly clear that widespread application of rodenticide does not curb rat populations,” says Jason Munshi-South, an ecologist and rat expert at Drexel University in Pennsylvania. “What it does is kill rats on a local level, so it feels like you’re doing something. But you’re up against the brutal math of rodent reproduction.”
A well-fed mother rat can have 10 or more babies in a litter, and have several litters a year. Plus, poison doesn’t reach every rat, and some have learned to avoid it.
What poison does do is cause gnarly deaths for rats—often leading to prolonged internal bleeding—and it kills other wildlife, too. When scientists collect dead birds of prey, they find rodenticide in most of them. “Dying from rodenticide like an anticoagulant is a terrible way to die,” Munshi-South says.
Exterminators continue to rely heavily on poison and baits in part because it’s easy, Richardson says. “They’re just doing what they have the capacity to do in a practical, short time frame,” he says.
The status quo is also benefiting the extermination industry.
“Exterminators don’t get paid to remove rodents entirely,” Parsons says. “They get paid to control rodents so that they’re always needed. I’m not at all cynical. This is just the way it works.”
by Benji Jones, bioGraphic | Read more:
Image: anatolypareev/Shutterstock
