Mouse poisons and baits
What you should know before buying poison to combat cottage rodents
Snap traps won’t protect your cottage for the whole winter, since once a trap is sprung it won’t work again without being reset. Which is why professionals recommend using anticoagulant poisons such as warfarin and bromadiolone (marketed as Bromone), if you’re going to be away from the cottage for long periods. The anticoagulants work by inhibiting the production of a clotting protein in the liver. The mouse’s blood becomes so thin that it leaks out of the blood vessels. Contrary to popular assumption, studies indicate that this is a relatively humane way to kill. “If we could talk to the mouse he would say, ‘Well, I’m feeling kind of lethargic,” says Robert Corrigan, a consultant at RMC Pest Management Consulting in Indiana and one of North America’s leading experts on rodent control. “Then he would go to sleep and die.”
But will he take anyone with him? Small doses of warfarin won’t harm adult humans. In fact, it’s used as a heart medication. But warfarin and the more powerful bromadiolone can do serious harm to children and pets. For safety, it’s best to use poisons in baiting stations or buy pre-baited stations (available in some hardware stores or from pest-control companies). Stations are also more effective, since mice prefer to eat in an enclosed space. Todd Summers, service manager for Orkin Pest Control in Scarborough, Ont., suggests you make a map in the fall showing all poison locations and clean up as soon as you arrive in the spring, or whenever small, indiscriminate eaters are dropping by. Make sure your store of poison is also out of the reach of kids and pets.
What does Harry Rowsell, founder of the Canadian Council on Animal Care, use to control mice at his cottage near Fenelon Falls? Warfarin in seed, block or pellet form, not only because it’s effective, but because, like many experts in animal care and pest control, Rowsell believes that anticoagulant poisons are the most humane method for rodent control. As a veterinary pathologist and retired professor at the University of Ottawa, Rowsell has the research to back his opinion. In one study on rats, Rowsell, whose specialties include animal euthanasia, placed electrodes in the brain pathways for pain, then fed the rats anticoagulants. “We didn’t see the kind of excitation patterns you see with pain. You get a slow demise, and a slow flattening of the electroencephalogram, indicating brain death. It does take a few days but the animal is not in a disturbed state.”
Some people, such as Christine Mason, wildlife coordinator for the Ontario Society for the Prevention of Cruelty to Animals (SPCA), believe that poisoned mice who head outdoors could end up as a deadly lunch for owls, hawks, foxes, and raccoons. But as Ron Brooks, who works with deer mice in the zoology department of the University of Guelph, points out, “Owls and hawks wouldn’t touch a dead mouse, much less eat it, though maybe a cat or weasel would. But even if an owl was to eat a couple of poisoned mice, it’s not likely it would be harmed because mice are so small.”
And what happens to the corpus delicti? Follow your nose. The mouse may take its final nap under your sofa or, less conveniently, curled up in the insulation. Just how bad the resulting odour can be is a matter of opinion. Some experts, like Brad Gates, claim that poison reduces the smell, but he warns, “This chemical isn’t magic… it can still be quite unpleasant.” If the mouse dies in a cottage during the winter and isn’t anywhere near a heat source, smell probably won’t be a problem. But if he dies during the summer, in a nice warm spot with a breeze passing by, you may remember him for quite a while.
This article was originally published on May 23, 2005