Common Signs You Still Have Mice or Rats in Your Home

rodent degu
ValeriMak / Getty Images

You had a problem with mice or rats in your home, but you think that you—or the pest management professional you called in—got rid of all the rodents. But how do you know for sure? Are those droppings you found under the cabinets old or new? Do those gnaw marks you just found mean that you have more mice or rats, or are they from an old infestation? Examine the classic signs of rodents closely to determine whether you have a current or previous infestation in your home.

Is It Mice or Rats?

If you see them, it's usually easy to distinguish adult mice and rats by their size alone. Mice are only about 7 1/2 inches long, including their tails, while rats can measure up to 18 inches long. Juvenile rats can be similar in size to adult mice but have different physical characteristics. Rats have large heads (compared to their bodies), blunt or squared noses, and thick hairless tails. Mice have relatively small heads, pointy snouts, and thin hairy tails.

You can also distinguish mice from rats by their droppings. Mouse feces are about 1/8 to 1/4 inch in length and have a smooth shape with pointy ends. Rat feces are about 3/8 inch long and 1/8 inch in diameter and have blunt, rounded ends.

Rodent Droppings

New droppings are dark and moist. As droppings age, they dry out and become old and gray and may crumble if touched. Droppings are most likely to be found near food packages, in drawers or cupboards, under sinks, in hidden areas, and along rodent runways (common travel routes).

You will find the greatest number of droppings where the rodents are nesting or feeding, so inspect the area around newly found droppings to determine whether there is still an active—or new—infestation.

Animal Gnawing

In contrast to the droppings, newer gnaw marks will be lighter in color and become darker as they age.

These are often found on food packaging or the structure of the house itself. One way to determine age is to compare a gnaw mark you recently noticed with those on a similar material that you know are older. If the newly found marks are lighter in color, it could be an indication of a continuing infestation. The marks can also indicate whether you have rats or mice: Larger gnaw marks are likely to have been produced by the larger teeth of rats. If you had a mouse infestation but are now seeing larger gnaw marks, you may now have rats. And vice versa.

Foul Odor

Cats and dogs (or even a pet rat or mouse) may become active and excited in areas where rodents are present. This is a result of the odor of the rodents and is most likely to occur when rodents have recently entered a structure. If you see your pet pawing at an area in which it had previously had no interest, get a flashlight and examine the area for rats or mice. (If you simply find a lost toy or pet treat, count yourself lucky on this one!) If an infestation is large, you may also detect an ongoing stale or musky smell coming from hidden areas, indicating an active infestation.

Mouse Tracks and Runways

If rodents are currently active in or around your home, their runways or tracks are likely to be more distinctive, as they become fainter as time passes.

Tracks or runways are most easily detected with a flashlight or blacklight held at an angle toward the suspected area. You may see smudge marks, footprints, urine stains, or droppings. If you suspect an area is being frequented by rodents, try spreading a very thin layer of flour or baby powder over the area. If rodents are active, you are likely to see their trails in the powder.

Rat (or Mouse) Nests

Rodents will use materials, such as shredded paper, fabric, or dried plant matter, to make their nests. If these areas are found and have any of the other signs of current presence (fresh droppings, gnawing, odor, or tracks), it is likely that there is still an infestation in your home.

Sounds

Mice and rats commonly nest in the spaces between framing members in the wall, floor, and ceiling structures.

These homes are right up against the drywall or other surface material, so it's common to hear scratching against the drywall, particularly at night when the animals are most active. Scratching sounds also are commonly heard as mice or rats travel inside house structures. Frequent and prolonged scratching throughout the day and night may indicate that a rodent is stuck and trying to escape (they can get stuck in wall cavities despite their superb ability to climb most surfaces).

Signs of Rodents in Your Yard

Rodents are attracted to piles of trash, organic waste, and similar materials for both food and nesting. If collections of trash or debris are present near the home or structure, inspect them for signs of rodents. If there is no indication of rodents, it is likely that the animals are not coming into your home, either. But if you do have such piles present, eliminating them can help prevent future rodent problems.

Rodent Population Size

Certain signs can also indicate the size of a population. If rodents are seen at night but never during the day, the population has probably not gotten too large and can be controlled with traps and bait. If you are seeing any rodents during the day as well as numerous fresh droppings or new gnaw marks, it is likely that the population has gotten quite large and may require professional services.