Catching sight of a scurrying rat when you are heading out to weed the dahlias or gather tomatoes is one of the most unsettling things that can happen in the garden. The most stalwart gardener may reach for the phone to call the exterminator. We want those rats gone.
But let’s take a moment and see who we are up against. The rat you are likely to encounter in your garden is Rattus norvegicus, the Norway rat. Norway rats have traveled the world and happily settled on every continent except Antarctica. They live 12 to 18 months and are social, secretive, intelligent animals.
Males and females live in separate, hierarchical colonies (a large group of rats is called a mischief), and females den closer to the food source. They may have five litters a year, averaging seven kits per litter. Norway rats are excellent climbers and expert tunnelers. Tunnel entrances are four inches across, angled at 45 degrees, and often have a mound of dirt at the entrance. (Chipmunk tunnels are two inches in diameter and go straight down.) Rats have poor vision and use walls or tree roots as guidelines — helpful information for placing traps.
Rats are omnivores, eating anything and everything, including songbird eggs and chicks. They do not hibernate, but they dislike cold temperatures and require a water source, which explains their predilection for sewers. Human habitation is the perfect environment for rats.
What to do?
Exterminators, true to their name, will bring poison to your property that will kill rats. One of the selling points for poisoning is that the customer rarely finds the victims; with mechanical traps, someone has to remove the bodies. Poisoning options include second-generation anticoagulant rodenticide (SGAR) and cholecalciferol.
SGARs will be set about your property in black bait boxes, which allow rats and other small animals to eat the bait. Symptoms of hemorrhaging blood vessels appear some time after consumption. Slow-moving and bloated, poisoned animals are easy prey for predators.
Tough luck for the targeted rodent, but worse luck for the rest of us because anticoagulant rodenticides never break down after being introduced into the environment. They accumulate in the food chain, the soil, and the water supply. Predators that catch and eat poisoned rodents are poisoned; the toxins accumulate in their systems until they are killed outright or are so debilitated they are unable to survive. These non-target species could be hawks or owls (just the animals you want to control rodents); they might be foxes, coyotes, opossums, raccoons, or even snapping turtles. Or they might be house cats. Or the family dog. And it is not just animals who are affected. A glance at the literature reveals that in Massachusetts between 2021 and 2023, nearly 200 cases of human anticoagulant rodenticide poisoning were reported, almost half involving children under the age of six. Rats are a real issue. But anticoagulant poisoning is not the solution.
The second bait box poison option, cholecalciferol, is an overdose of vitamin D3. Symptoms appear over time as the organs calcify, a slow and agonizing death. Predators that eat cholecalciferol-poisoned animals do not seem to be adversely affected.
There is a third, non-toxic, bait box option: rodent contraceptives. Roll your eyes if you like, but rodent birth control is effective at reducing the rat population. Bait boxes must be checked regularly to keep them adequately supplied; refill frequency depends on your resident rat population and may take some adjusting. Consistency is key! There are two formulations, liquid or solid. A gardening acquaintance, with a large and productive vegetable garden, tells me the solid worked best for her (and doesn’t freeze).
Belmont has opted out of using SGARs on public properties. But unless and until the state bans them, private contractors and businesses are still able to use SGARs. If you contact an exterminator, ask them which rodenticides they offer and tell them you do not want SGARs.
So you have options for bait boxes. There are additional steps you should take to make your property less appealing and possibly keep rats from encroaching in the first place. Keeping things tidy will deter them. If you have a compost pile, turn it frequently; rats will not get a chance to settle in and you will speed up the composting process — a win-win.
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The number one thing you can do to discourage rats is reduce their access to food. Take care when filling bird feeders and consider removing them altogether. Do not put food out for squirrels or other mammals, wild or domestic. Food waste is a major lure, as is pet waste, so pick up after your dog. Use a curbside composting service for food scraps to keep food out of the trash. Be mindful about securely closing compost and trash bins and be diligent about getting them to the street on pickup day.
If you notice overflowing trash bins, or if you see a rat, contact the Belmont Health Department at 617-993-2720.
And talk to your neighbors. Chances are, if you have seen a rat, so have they. Working together to devise a plan of action and implement it will bring the best results; rats don’t know property lines.
Dorothy gardens in Belmont where she lives with her husband, Steve, and their two dogs, Rosie and Jasper. She has six grandchildren — all perfect by definition — and has enjoyed introducing them to gardening. She has an abiding interest in nature and is always amazed by the wonders to be found in her own backyard.
All photos by Dorothy Gilman
