Wednesday, February 24, 2021

Oh, Rats! Controlling populations starts with prevention

ratsIt must be hard to foster a decent public image if your family was responsible for spreading the plagues across Europe, Asia and North Africa that killed between 75 and 200 million people. If rats were able to launch a rebranding campaign, it would never work. I imagine that even would throw up their hands and give a refund.

But in spite of the many problems they cause, rats do have a few entries in the positive side of their ledger. In a CBC Radio interview, Bobby Corrigan, a renowned NYC rodentologist (yes, there is such a thing) said rats are “the most important mammal group to homo sapiens.” In addition to being test subjects for innumerable studies on human diseases and new drugs, rats have provided insights into our neurology which may not otherwise have been made, especially the way richness of environment affects brain development. They can sniff out land mines better than any human technology, and can accurately tell if a patient has tuberculosis.

They have other fans aside from researchers:  In northwestern India at the Karni Mata Temple, some 25,000 rats are revered as holy descendants of a Hindu goddess, destined to be reincarnated as holy men. Or at least the males are.

On the other hand, nearly everyone on the planet shudders at the thought of these rodents. Variously called sewer, wharf, or Norway rats, brown rats (Rattus norvegicus) originated in Mongolia. They are dark brown to black, measure between five and eleven inches long (the tail being slightly shorter), and weigh from five to eighteen ounces. Endowed with an uncanny intellect and an unparalleled adaptability to new habitats, rats also have a powerful burrowing instinct.

Rats have a reputation – not wholly deserved – as cunning, hostile, dirty, disease-ridden breeding machines (to be fair, that’s likely how other animals view us). Their colossal creepiness quotient is partly due to their tenacity – they can eat almost any organic matter, chew through concrete, tread water for three days, and fit through a hole the size of a quarter. As Vancouver-based researcher Dr. Chelsea Himsworth notes, rats can indeed be “sponges” for human pathogens like C. difficile and MRSA, but admitting that “There’s surprisingly little known about rat populations or the health risks they pose.”

Their ability to multiply and be fruitful is unnerving, too:  rats are sexually mature at three months, and healthy females come into heat each 4-5 days thereafter. After just three weeks of gestation, they birth a litter of 8 to 12 pups. With an average 9.5-month lifespan, a female can easily have twelve litters totaling 96-144 offspring. And by the end of her life, eight of her litters will be breeding already. Yikes.

Given all that, and the fact rats have been around for some 56 million years, it’s pretty clear they will always be with us. We’d like to keep them away from our homes, though, and to moderate their numbers. But we’ve trapped, shot, and gassed them, and baited them with every known toxin. We’ve set cats (and the Middle Ages, priests) upon them, all to no avail. With rat populations predicted to rise as a result of climate change, we clearly need a better strategy.

An ounce of prevention, as they say, is worth a kilogram of cure. We’ve long known economic justice is a far cheaper, and infinitely more effective, way to create and maintain global peace than all the armies in the world, yet nobody wants to put money toward such ends if we can’t see immediate results. Urban rodentologist Bobby Corrigan sees this dynamic with rat control. “To manage rats, you manage an environment. Putting out poison baits and trying to kill them every single day will go on forever and you’ll end up in the same spot,” he explains. He says we need to start in “peacetime” to control rats. Easier said than done. If I see a rat in the house, for sure I’ll wage war on it. But would I rat-proof my home otherwise? Hmm.

“More humans means more trash,” Corrigan notes. In cities and villages, if there’s a food source, rats will find it. This can be true in the country as well – visit any farm with silos or grain-storage bins, and you’ll almost certainly find rats, even if homes in the region are not infested. Lucinda Cole, a researcher at the University of Illinois, told CBC Radio The Current host Anna Maria Tremonti that “rat presence is a barometer reading of environmental health of a neighborhood.”

Securing garbage and composting responsibly are critical for rat control. In terms of buildings, inspect places where power, cable, sewer and phone pass through the walls. Look at dryer vents, and be sure attic vents are screened properly. Watch for signs of burrowing, especially next to foundations, and listen for any movement within walls. “Rat o’clock,” or sunset plus two hours, is the time they are most active. Also look for rat fecal pellets – they drop 50-60 per day, everywhere they go. Corrigan says rats like to “hugger-mugger” into small spaces, and that a typical rat’s nest is the size of a basketball.

As you wander around envisioning all the places on your property large enough to hide a basketball, keep in mind that rats are the first animal in the Chinese Zodiac, denoting, intelligence, wealth, and (of course) fertility. Then again, 2020 was the year of the rat, so that may be a poor example.

Paul Hetzler is a naturalist, arborist, and author. He’d rather not say whether his home has been rat-proofed.

Photo by Jason Snyder, CC BY 2.0, via Wikimedia Commons

Related Stories

Paul Hetzler has been an ISA Certified Arborist since 1996. His work has appeared in the medical journal The Lancet, as well as Highlights for Children Magazine.You can read more of his work at or by picking up a copy of his book Shady Characters: Plant Vampires, Caterpillar Soup, Leprechaun Trees and Other Hilarities of the Natural World


3 Responses


    There was an amazing article in the National Geographic on these most interesting animals. I some countries rat on a skewer is a lunch treat.
    I don’t get all skirmish about them and just view them as I view the large family of squirrels in my yard. More or less the same with different tailes.

  2. Anthony o says:

    Love, LOVE Rats! They are highly intelligent beings and great to have as a companion. Rats are extremely clean animals and spend the majority of their time cleaning themselves. More than people do! The problem here is lazy slobs of people that do not pick up their trash or clean up after themselves. And maybe they should take some time to rat proof their house. Another sign of laziness!
    And the use of poison?? Just another opportunity to kill more animals that will kill or consume the Rat,,