Do Rats Eat Mice? What It Means for Mice and Rats in Your Home

TL;DR

• Yes. Norway rats and roof rats can kill and eat mice when they get the chance, though not every rat hunts mice.
• Mice treat rats as predators, so they tend to avoid rat odour and may spend less time looking for food where rats are active.
• You can have mice and rats at the same time, but it is uncommon and usually takes a large food supply and plenty of space.
• Compare droppings: mouse droppings are usually about 1/8 to 1/4 inch long and pointed at both ends, rat droppings about 1/2 to 1 inch long and blunt at one end. Both sizes in different spots can mean both rodents.
• Seal to the mouse standard: a gap that stops a rat will not stop a mouse. UC IPM recommends sealing all holes larger than 1/4 inch.
• Need help? Get a quote from a recommended local exterminator through Pest Agent's referral form.

Rats do eat mice: Norway rats and roof rats kill and eat them when the chance comes up, and mice keep clear of the rooms where rats are active. That rivalry has an odd side effect for homeowners, since clearing out the rats can leave an opening for the mice that were keeping their distance.

It is also why finding both species in one house is the exception. Not every rat is a mouse killer, though, and lab tests show how much that habit varies from one rat to the next.

Do Rats Eat Mice?

Rats do eat mice: Norway rats and roof rats are omnivores that kill and eat mice when they get the chance, and they also compete with them for the same food and shelter. Not every rat hunts mice, but the behaviour is well documented in both the lab and the field.

What Do Rats Eat?

Rats eat almost anything, and meat is on the menu. UC IPM lists cereal grains, meats, fish, nuts and some fruits in the diet of Norway rats. According to the University of Michigan's Animal Diversity Web, Norway rats tend to prefer meat when given the option, and their prey can include chicks, mice, birds and small lizards. In a house, most of what a rat eats comes from stored food, garbage and pet food, but a mouse that crosses its path is a potential meal.

What Lab Studies Show About Rats Killing Mice

Lab studies show that many rats kill mice, but not all of them. Scientists call the behaviour muricide. In one study of rats from 15 laboratory strains, the share of males and of females that killed a mouse ranged widely depending on the strain (Walsh, 1982). In other words, some rats almost always attack mice, while others leave them alone.

Do Roof Rats Eat Mice?

Roof rats eat mice too. In captive trials published in the journal Animal Behaviour in 2013, most ship rats (another name for roof rats) were aggressive towards mice, and rats that interacted with a dead mouse usually ate at least part of it. Rats that were kept hungry tended to eat more. The researchers concluded that the behaviour resembles predation, and a related University of Waikato thesis describes ship rats as viewing house mice as prey that they eat when the opportunity comes up.

Do Rats Eat Dead Mice?

Rats do eat dead mice, as the same captive trials showed. In a home, this means a mouse caught in a trap or killed by bait can become food for a rat. Mice can also feed on their own dead, which our guide to whether mice eat dead mice explains.

How Do Mice React to Rats?

Mice treat rats as predators, so they avoid rat odour and spend less time looking for food where rats are active. This reaction is the main reason the two rodents rarely share the same space.

Mice Avoid Rat Odour

Mice avoid the smell of rats. AnimalKind, the BC SPCA's animal welfare accreditation program, notes that house mice tend to avoid areas where Norway rats live because Norway rats are considered their predators. Canadian wildlife control companies report the same thing: mice are afraid of rat odour because rats typically kill mice.

Mice Forage Less Near Rats

Mice forage less when rats are nearby. In captive experiments at the University of Waikato, house mice avoided caged rats, and in the field, mouse foraging may have been limited by the risk from abundant ship rats (Bridgman, 2012). A mouse that is busy avoiding rats eats less, explores less and stays out of the rats' areas.

Mice Increase When Rats Are Removed

Mice often increase after rats are removed. Field research in New Zealand found that where ship rats were controlled, house mice tended to be detected more often and mouse activity tended to rise (Bridgman, 2012), and the New Zealand Journal of Ecology notes that mouse populations can grow after larger introduced mammals are controlled (Wilson et al., 2018). These studies took place in forests, not houses, but they explain why some homeowners notice mice soon after a rat problem is solved.

Can You Have Mice and Rats at the Same Time?

You can have mice and rats at the same time, but it is uncommon, and it usually takes a large food supply and plenty of space. Rats kill mice and mice avoid rats, so a small house rarely holds a stable population of both.

When Mice and Rats Live Together

Mice and rats live together mainly where there is a lot of food and room to spread out. Canadian wildlife control companies say that often only a very large supply of food and habitat can support both types of rodents, and that the two species can share one area when the habitat is large enough and food is plentiful. That makes it more likely in large spaces, such as farm buildings, warehouses or a property with several outbuildings, than in a typical home.

Where Each Rodent Settles in a Building

Each rodent tends to settle in a different part of a building when both are present. If a basement or attic suits both species, the rats will likely win that space, according to a Kitchener wildlife control company, so mice tend to end up in other areas. UC IPM notes that when Norway rats and roof rats share a building, Norway rats typically stay in the basement and ground floors while roof rats tend to occupy the upper floors. Signs in two separate parts of a property can therefore mean two different rodents.

Rats in Canada

Rats are not found everywhere in Canada, which changes the odds of having both. Health Canada lists the house mouse, the deer mouse, the Norway rat and the roof rat among rodent pests. Alberta says it has been rat-free since 1950, when its Rat Control Program began: there is no resident population of rats, it is illegal to own pet rats there, and the province asks you to report any rat you see (310-FARM in Alberta). In British Columbia, Norway rats and roof rats have been present since about the mid to late 1800s and are generally well established in the Lower Mainland, Vancouver Island and the Gulf Islands, with newer populations in the interior, including the Okanagan Valley and Kamloops. If you live in Alberta, a rodent in your house is almost certainly a mouse.

How Can You Tell If You Have Mice, Rats or Both?

Mice and rats leave different signs, so size, droppings and how far the animals travel tell you which one you have, or whether you have both. Our full guide to mouse vs rat identification goes into more detail.

Body Size

Body size is the quickest clue. An adult house mouse weighs about 1/2 ounce (about 14 grams), according to UC IPM, and usually measures around 5 to 7 inches (about 13 to 18 cm) including its tail. A Norway rat has a stocky body and a blunt nose, and adults often weigh around one pound (about 450 grams), according to the University of Arizona. A large mouse can look like a young rat, so check the proportions: a young rat usually has a bigger head and bigger feet for its body, and its tail is often shorter than its head and body together, while a mouse's tail is about as long as its head and body.

Droppings

Droppings are the easiest sign to compare. House mouse droppings are 1/8 to 1/4 inch long (about 3 to 6 mm) and pointed at both ends, while rat droppings are usually 1/2 inch (about 13 mm) or longer and blunt at one end (University of Arizona). Finding both sizes in different spots is a sign you may have both rodents. See our guide to mouse poop vs rat poop for photos and details.

Noises at Night

Noises at night tell you that rodents are active but not which kind. Health Canada lists scampering and scratching sounds in the walls at night as a sign of rodents. Burrows or holes near foundation walls point more towards Norway rats, which often nest in underground burrows next to foundations and under debris piles.

Travel Distance

Travel distance helps you find where each rodent lives. House mice seldom venture more than around 30 feet (about 9 metres) from their nest and food, while Norway rats may forage much farther from their nests each night, according to UC IPM. Mouse signs stay close to one area, often a kitchen or a storage room, while rat signs can lead outside to a burrow, a shed or a garage.

Reaction to New Objects

Reaction to new objects is another difference. UC IPM notes that rats tend to avoid new objects and new foods, while pest control companies describe mice as curious explorers that check out anything new. If a new trap catches a rodent the first night, it is more likely a mouse. If traps sit untouched for days while signs continue, a cautious rat may be avoiding them.

How Do You Get Rid of Mice and Rats Together?

Getting rid of mice and rats together means sealing gaps small enough to stop mice, setting traps sized for each rodent and following up after the rats are gone. The basics are the same for both, but a few details change.

Seal Entry Points

Sealing entry points has to be done to the mouse standard, because a gap that stops a rat will not stop a mouse. Health Canada says mice can squeeze through a crack about the size of a dime and rats through a quarter-sized hole. UC IPM recommends sealing all holes larger than 1/4 inch (about 6 mm) to keep out both rats and mice, and notes that a rat may get under a door with a gap of about 1/2 inch (about 13 mm). Use metal weather stripping, patch foundation cracks and put fine mesh over vents. Our guide to finding mice entry points walks you through it.

Food Storage

Food storage takes away what draws both rodents in. Health Canada recommends storing dry food and dry pet food in metal or glass containers, rather than in bags or boxes. Clean up crumbs, keep garbage in a closed bin and bring pet food in at night.

Trap Size

Trap size matters when you have both rodents. UC IPM warns that mice and small young rats may not trigger a rat snap trap, so a rat trap alone can leave the mice untouched. Use mouse traps where you see mouse signs and rat traps where you see rat signs, placed close to walls, behind objects and in dark corners. Health Canada advises checking all traps daily. Learn how to set a mouse trap or compare the best mouse traps.

Rodenticide Safety

Rodenticide must be used with care around children and pets. Health Canada and the Government of British Columbia say poison baits must be placed in a tamper-proof bait station wherever children and pets can reach, and Health Canada warns that anticoagulant baits are usually highly toxic. Only buy products with a PCP registration number on the label, which shows the product is registered by Health Canada, and follow the label exactly. Pick up dead rodents quickly with gloves, so pets and children cannot reach them.

Cleaning Up Droppings

Cleaning up droppings safely protects your health, because mice and rats carry disease, and Health Canada notes that the deer mouse is the most common carrier of hantavirus. Wear rubber gloves and a dust mask, dampen the droppings with a bleach and water solution, then wipe them up. Never sweep or vacuum dry droppings, since the dust can make you sick. Our step-by-step guide on how to clean mouse droppings covers the details.

Monitoring for Mice After Rat Control

Monitoring for mice after rat control keeps a new problem from building up. Mice may increase once rats are gone, so keep a few mouse traps set in quiet spots for several weeks after the last rat sign, and watch for small, pointed droppings. If mice appear, act early, while there are only a few.

When to Call a Pest Control Professional

Calling a pest control professional makes sense when you find signs of both rodents, see burrows near your foundation, or keep finding fresh droppings after a few weeks of trapping. A licensed professional can confirm which species you have and treat each one. Our guide on when to call an exterminator for mice lists the warning signs, and you can get a quote from a recommended local exterminator through Pest Agent's referral form. For more rodent guides, visit the mice hub.