How to Kill Rats, Inside and Outside
Where Modern Humans Go, Rats Follow
The brown rat (Norway rat) and black rat (roof rat) have followed Europeans and their food supply to almost every place on earth, including, of course, California's Bay Area, where both kinds of rats are abundant.
Our Trouble With Rats
Rats seek food, shelter, and water. Where these three things exist, you'll find rats.
We live in San Mateo County in a canyon that has been invaded by ivy and blackberry tangles and generously planted with fruit and nut trees, providing shelter and food for rats.
And sure enough, over the years, at our house we had:
- Rats in the garage, living in the washer and dryer, attracted by dog food
- Rats in the outside barbecue, attracted by the drippings
- Rats inside the house, attracted to food and water under the kitchen sink
- Rats outside, attracted by birdseed in the feeders
How to Get Rid of Rats, Indoors and Outdoors
We have learned over the years that the way to get rid of rats is:
- Kill all your indoor rats with the Rat Zapper, which humanely executes them and allows you to easily dispose of their carcasses.
- Remove, clean up, or lock up outdoor rat food sources such as barbecues or dog food.
- Seal off any entrances that allow rats to get into your house to look for food.
- But give up on the idea that your suburban outdoors can be rat-free. Expect to see rats outside once in a while. Let predators do their part to limit the rat population.
Rat Control Methods Discussed Below
3. Rat Zapper
4. Other Rat Control Ideas
- Glue Traps
- Live Traps
- Cats and Dogs
To kill rats, we have tried poison, traps, and a “Rat Zapper,” a battery-operated device that electrocutes rats. All have their advantages and disadvantages. which we discuss below. We are most impressed with the Rat Zapper.
1. Our Experience with Rat Poison
Advantages: Rat poison will definitely kill rats. Until recently, in California, you could buy rat poison in large green pellets made by D-con and others. We tried it. Rats found the pellets very appetizing; they hauled them to their nests. As they ate the rat poison, it killed them slowly, from internal bleeding. We could tell that they were eating the poison because the poop the rats left behind turned from hard pieces to a runny green liquid.
If poison is used indoors, the poisoned rats may die indoors and have to be extracted from small spaces before they cause an odor. The pellets are poisonous to humans and pets, and the contaminated green poop had to be cleaned up carefully.
It turns out the main issue with these green pellets is their danger to wildlife and pets. Since most rat poisons are slow-acting and long-lasting (see an explanation of this at the end of this article), poisoned rats dead or alive are also poisonous, and if sick or weak can be eaten by cats, dogs and wildlife—bobcats, lions, coyotes, hawks— who can in turn be poisoned.
The EPA banned slow-acting anticoagulants packaged for household use, like these green pellets, in 2015. These and similar chemicals are still being used by professionals, though, and they are still a danger to wildlife. Furthermore poisons can't totally get rid of outdoor rats. Even though the county maintains rat poison dispensers in our creek, we still see rats on the deck now and then.
I would not use rat poison now, partly because of the wildlife issues, and partly because the Rat Zapper is so effective at killing indoor rats.
2. Our Experience With Rat Traps
Rat traps work well, indoors and outdoors. Traditional rat traps, like in the video, are spring-loaded, with a trigger you attach bait to. I baited one of these with peanut butter and set it under the kitchen sink. In the middle of the night I heard a loud “slap," and knew I had caught a rat. In the morning, I went to the rat trap to see blood all over the inside of our kitchen cabinet, and in the corner, a large mutilated rat. I had to scoop the rat out with a shovel and place it in a bucket.
- Rat traps usually kill rats.
- Rat traps don’t always kill. Rats can escape maimed from a rat trap and suffer. If you find the rat, then it's up to you to kill it with a shovel or by drowning. I purchased a pellet gun to shoot the injured rats instead of doing it by hand.
- Rat traps may cause a distressing mess. A dying rat may drag the trap around, leaving a trail of blood and guts to be cleaned up.
Video: Rat Trap Demonstration (Don't Worry, Using Pencils and Carrots)
3. Our Experience With the Rat Zapper
My brother introduced me to the . You put some bait in the reusable trap, and when the rat walks into the trap, electricity—8000 volts—from the batteries electrocutes the rat in a few seconds. Then, all you do is dump the rat out of the trap into the garbage. Rat Zapper
My father-in-law had a rat problem: rats were getting into his hot tub, and making a new nest in the cabinet of his barbecue every few days. I sent him a Rat Zapper as a gift and he reports that he killed over 50 rats with it. Presumably he replaced the batteries several times, because four AA batteries are only supposed to be good for about 20 kills.
Biconet, which sells the Rat Zapper and other integrated pest management tools, argues that a zapper it is safer to use around children and pets than poison or traps, because its entrance is designed to admit nothing bigger than a rat. If a dog or child does put a paw or finger inside, the electric shock should trigger a reflex causing the child or dog to pull away from the trap.
I think the Rat Zapper is the way to go.
- Kills rats instantly—doesn't leave them wounded.
- Dead rats are easy to find and dispose of.
- Doesn't poison the environment.
- Uses a lot of batteries.
- Not designed for outdoor use (though it can be used outdoors covered with a plastic bag or tarp to keep moisture from shorting it out).
That the Rat Zapper is designed for indoor use doesn't matter much, because it's more important (and more realistic) to get rid of indoor rats than outdoor ones, as we explain below.
Video: Rat Zapper Demonstration
4. Other Rat Control Ideas
People on the internet mention other rat control ideas, but few say they work well.
Glue traps catch rats, but don't kill them: that dirty job is left to you. PETA and Friends of the Earth say glue traps are cruel and catch non-target creatures.
Rat repellents like peppermint oil, ultrasonic devices, and night lights don't seem to be reliable. Rats may avoid these nuisances for a while, but when they decide they aren't dangerous, they will go back to looking for food like they usually do.
Humane traps (live traps) have mixed results. The rats may figure out how to dodge them, and you have to figure out what to do with the live rat you catch.
Using Cats or Dogs to Control Rats
Cats will hunt rats, but some cats won't tangle with large Norway rats, for their own safety no doubt.
Dogs have been bred for hundreds of years to help humans deal with rats. They catch the rats, bite them, and then shake them until they're dead. It's pretty gruesome to watch, but I could see hiring dogs to kill rats if I had a huge rat problem.
Ratproofing: Making Your Indoor Space Defensible Against Rats
Know Your Enemies
First, understand these two species that go to so much trouble to get hold of human and pet food.
Norway Rats or Brown Rats tend to stay low, are good diggers and swimmers, and use basements and sewers to invade houses. They like meat and get into barbecues. Their turds are more rounded than roof-rat turds (see one of the pictures above). In the 19th century, stagers of rat-and-terrier fights used to keep the prettiest Norway rats ("fancy rats") and tame them, and they are the ancestors of today's pet rats and lab rats.
Roof Rats or Black Rats are smaller and better climbers. Roof rats tend to stay high, nesting in trees and woodpiles, and using tree limbs and powerlines for travel. They can range 300 feet or more from the nest, living in one backyard and feeding in another. They love backyard fruits and nuts. They may invade attics.
Both kinds of rats are clever at staying out of sight, and at avoiding new things in the environment that might be traps or hazards.
Secure the House to Keep Outdoor Rats Outdoors
The University of California at Davis Integrated Pest Management Program, our San Mateo County pest control agency, and the Centers for Disease Control all have advice on how to close off openings that rats might use to enter a house. The idea is that you can't hope to eliminate rats in the great outdoors—humans have never been able to do that—but you can minimize some outdoor temptations like dog food and barbecue grease, and you can separate the human space indoors from the rat space outdoors.
If you close off all openings to the basement or crawlspace, around the pipes, and the bottom of the house, and leave no holes larger than a half dollar, you can theoretically keep the Norway rats out; and if you can do the same for the attic and roof area, and leave no holes bigger than a quarter or so, you can keep the roof rats out. Also, you can
- clear vines and shrubbery away from the bottom of the house, so rats can’t hide right next to the house;
- raise your woodpile up off the ground;
- and remove tree limbs within three feet of the house so that roof rats can’t use them to leap onto your house.
Then if you keep food sources inside the house cleaned up, or secured in chew-proof containers, at least for a few days, you can get any rats already inside the house to kill themselves with the baited zappers or traps you set out, and no more will come in. End of indoor rat problem.
Ratproofing: Managing the Outdoor Rat Problem
Problems arise when the boundaries between the inside and the outside of the house are kind of fuzzy. We humans find it convenient to go in and out of the house with our food and food for our pets.
Rats will get what they can from our garbage cans, compost piles, barbecues, and bird feeders. The best long-term strategy is to minimize these outdoor sources of food, while sealing off your house so rats can't get to indoor food sources.
Dog Food Attracts Rats
Dry dog food must seem ideal to rats; portable, storable, full of protein. In fact, it makes a good bait for rat traps. If the dog food is outside, or where rats can reach it, they will get it, and stash it in their nests, including in parked cars. Access to a large supply of cat and dog food can create a horrific infestation, as in this veterinary hospital where rats were able to get into the building and eat the pet food. Keep your dog food locked up, not in dishes on the porch or an open garage.
Barbecues Attract Rats
Rats in outdoor barbecues are clearly quite common. Lots of shaky YouTube videos show people screaming in terror when they lift the cover of a barbecue and a rat leaps out. Suggestions for making your barbecue a defensible rat-free space between grill sessions include:
- Cleaning it thoroughly.
- Burning off residue.
- Closing all vents and stopping all holes with aluminum screening, aluminum duct tape, or steel wool (though one writer says a gas grill will melt steel wool).
- Covering it with a zippered cover.
Why Poisoning Rats Is Almost Always Bad for the Environment
Killing rats with poison is a little more difficult than killing some other animals. Rats, like humans, are omnivores, and like humans experience the “Omnivore’s Dilemma” Michael Pollan describes: "What’s for dinner?" In other words, if anything might be good to eat, how do you know what is good to eat and what isn’t?
One way rats find out what’s good to eat is that they avoid gorging themselves on a food or bait they aren’t familiar with, a behavior called “bait shyness.” They sample a new food or food-like substance and see if it makes them or other rats sick before they eat any large amount. Rats do this cautious nibbling not only because they are clever and conservative, but because they are physically unable to vomit.
So poisons with a delayed effect are very effective on rats. The D-Con green bait pellets we used in the early 2010s were so effective for that reason: the poison, a second-generation anticoagulant rodenticide (SGAR), lasted a long time in their bodies, and only after a few days delay did it cause bleeding massive enough to kill them.
But since 2011 there has been ample evidence that this delayed effect of a buildup of poison in the rat's body, such as from second-generation anticoagulants, causes rats to poison other animals who eat them. The rats may not die for days after they start eating the poison. In the meantime, any cat or dog who eats the poisoned rat will be poisoned themselves, as will any bobcat, lion, fox, coyote, hawk, owl, or eagle. The California Department of Fish and Wildlife, explaining this problem in detail, confirmed 400 deaths in these wildlife species and many others from SGAR rat poisons between 1994 and 2014 and they say the effects are likely much more widespread since poisoned wildlife may hide and die out of sight. CDFW even found “tertiary” poisonings, two mountain lions who died from eating coyotes who had eaten poisoned rats.
The State of California banned four SGARs for household use in 2014, and EPA prohibited their marketing to households in 2015. EPA also prohibited the marketing of pellet-sized baits for home use (because the pellets might be eaten by children and pets). Lisa Owens Vianni of Friends of the Earth notes, however, that the 2014-2015 bans did not go nearly far enough to protect wildlife from anticoagulant baits. The four banned pesticides are still available for commercial or professional use—for example, in those bait stations you see in parking lots and malls and private property—and can still be bought online in quantity. Other long-lived anticoagulants like diphacinone ("Tomcat Liquid Concentrate") are still available for home use, and are toxic to wildlife. Anticoagulant rat poisons have been found in the carcasses of fishers (rare forest carnivores), spotted owls, and barred owls, and blamed for the deaths of suburban bobcats and mountain lions, even after the 2014-2015 law.
The National Park Service trapped this mountain lion, P-22 or "the Hollywood Lion," and treated him for mange (skin parasites) and anticoagulant poisoning. Two non-banned anticoagulants (diphacinone and chlorophacinone) were found in his blood samples. Anticoagulants seem to cause mange in bobcats, because the anticoagulants affect the immune system. P-22 has recovered from his mange, at least partly, but another Los Angeles lion, P-34, died of rat poison, and another, P-41 was found dead with residues of both banned and non-banned anticoagulants.
In 2018, a mountain lion was trapped just five miles from our house in San Mateo County. We don't know if this lion eats rats near bait stations in our neighborhood creek or elsewhere, but mountain lions do have large territories (100 miles on the average, according to mountainlion.org) and this lion was reported to have mange—a possible sign of anticoagulant poisoning.
Predators Could Be the Best Long-Term Solution for Rat Problems
So, it seems like the wrong approach, from a big-picture point of view, to regard the outdoors as an infinite source of rats who need to be poisoned if they come near people. Rats with abundant food and no predators will breed rapidly, but in nature they have predators who keep their population within bounds most of the time. If predators were encouraged, they could limit outdoor rat populations in the suburbs. But poisoning outdoor rats with anticoagulants kills the predators along with the rats, due to the long life and slow-acting nature of these poisons.
The only rat poison that has been found completely safe for consumption by humans, pets, and wildlife is RatX, a mixture of corn gluten and starch-like substances that absorb water in the rat's digestive tract. RatX kills rats from dehydration because rats, unlike other animals, are unable to vomit.
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