Mice and rats are omnivores that eat nearly anything available, from seeds and grains to insects, fruit, and scavenged meat. Their diets shift dramatically depending on where they live, but both species share a strong preference for calorie-dense, high-fat, and high-protein foods. Understanding what they eat can help whether you’re feeding a pet rodent, dealing with an unwelcome visitor, or just curious about these remarkably adaptable animals.
What Wild Mice and Rats Eat
In the wild, seeds and grains form the foundation of the diet for both mice and rats. When researchers tested food preferences in wild house mice, whole canary seed ranked as the most favored food, with oatmeal and wheat also well accepted. Beyond grains, wild rodents eat insects, larvae, snails, and whatever fruit or vegetation they can find. Berries like raspberries and blackberries are particular favorites for mice.
Rats, being larger, tend to eat a broader range of foods and are more likely to consume meat, eggs, and even small animals. Both species will eat carrion when other options are scarce, though they generally avoid flesh from their own species. In one study, hungry rats were significantly less likely to eat mouse meat if they had been raised alongside mice, suggesting social familiarity creates a learned food aversion.
City Rats vs. Country Rats
Where a rodent lives shapes what it eats more than almost anything else. Research comparing urban and rural rat populations in historic Canadian settlements found striking differences. City rats had consistently higher-quality diets with more animal protein, and their diets were remarkably uniform across individuals. That makes sense: urban rats feed heavily on human food waste, which provides a reliable, protein-rich food supply.
Rural rats tell a different story. Their diets varied widely from one individual to the next, with some eating mostly plants while others foraged more broadly. Without steady access to human garbage or food stores, rural rats adopted more diverse foraging strategies and ate lower on the food chain. Their diets overlapped significantly with raccoons, groundhogs, and other native wildlife, meaning rat introductions to rural areas likely increase competition for wild food sources.
Foods That Attract Rodents to Your Home
If you’re dealing with mice or rats indoors, it helps to know what draws them in. The biggest magnets are seeds, grains, and nuts. Birdseed left in feeders or stored in garages is a common lure. Any grain product stored in a cardboard box or paper bag is easy pickings, from cereal and rice to pasta and oats. Nuts of all kinds, including peanut butter, are highly attractive due to their fat and protein content.
Pet food is another major attractant. Rodents will eat dry kibble meant for cats, dogs, birds, or fish, especially if bowls are left out overnight. Sweet, high-calorie snacks like candy, chocolate, and jerky also draw them in. Fruit left on counters or fallen from backyard trees is fair game too. The key to prevention is storing food in airtight containers, cleaning up pet food at night, and keeping fallen fruit cleared from your yard.
How Rats and Mice Approach New Foods
Rats are famously cautious eaters, a trait called food neophobia. When a rat encounters an unfamiliar food, it goes through a deliberate process: extending its neck toward the item, sniffing and inspecting it with its whiskers, then taking only a tiny sample before retreating. If nothing bad happens, the rat gradually eats more over subsequent encounters. This behavior is one reason poison baits sometimes fail. Rats sample just enough to feel sick, then avoid the bait entirely.
Interestingly, this caution isn’t universal. Field research shows that rats living in rapidly changing environments, where food sources shift frequently, don’t exhibit the same neophobic response. They adapt to novelty and accept new foods more readily. Mice, by contrast, are generally more curious and less cautious about unfamiliar foods than rats, which is one reason snap traps baited with peanut butter tend to work better on mice than on wary rats.
What Pet Mice and Rats Need Nutritionally
Pet rodents thrive on a diet built around commercial pellets or lab blocks formulated for their species. For mice, a diet with roughly 14 to 18 percent protein and about 5 percent fat supports healthy growth and reproduction. Rats have similar needs. Higher protein levels (around 18 percent) are appropriate for pregnant or nursing females, while lower levels work fine for adult males and non-breeding females. Fiber is included in commercial diets to add bulk, but too much depresses growth. Around 7 percent dietary fiber is well tolerated.
Fresh foods make good supplements. Small amounts of vegetables like broccoli, peas, and leafy greens add variety and nutrients. Cooked egg, mealworms, or small pieces of chicken provide extra protein when needed. Fruits can be offered sparingly since their sugar content adds up fast for an animal this small.
Foods That Are Harmful to Rodents
Several common household foods are toxic or dangerous to pet rats and mice. The RSPCA lists onion, citrus fruits, walnuts, rhubarb, grapes, raisins, and chocolate as foods to avoid. Sugary and high-fat foods like dairy products should also be limited or skipped entirely. Raw dried beans contain compounds that are toxic to rodents before cooking. Sticky foods like peanut butter should be offered only in small smears, since large globs can pose a choking hazard for animals this size.
How Much They Eat and Drink
Mice eat proportionally more for their body weight than rats do. A mouse consumes about 15 grams of food and 15 milliliters of water per 100 grams of body weight each day. For a typical 30-gram mouse, that works out to roughly 4 to 5 grams of food and the same in water daily. Rats eat about 10 grams of food and drink 10 to 12 milliliters of water per 100 grams of body weight. A 300-gram adult rat eats around 30 grams of food and drinks 30 to 36 milliliters of water per day.
These numbers matter for pet owners portioning food and for anyone trying to understand how much damage a rodent infestation can cause. A single rat eating 30 grams a day contaminates far more food than it actually consumes, through droppings, urine, and gnawing on packaging. A colony of even a few rats in a pantry can spoil significant quantities of stored food in a short time.