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Signs of Rodents and How They Enter

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Common Rodent Entry Locations

Holes in vents can be access points for rodents

The general rule is, if you can fit your thumb in the hole, rats and mice can get in. To keep rodents out, you will need to find and seal ALL access points that are ¼ in or larger. The best places to look are:

  • Gaps around doors and windows. Garage doors should have intact weather stripping. Poorly-fitting windows and doors should be replaced or repaired. Windows that are opened should have screens.
  • Cracks in foundations and walls. Be sure to check all the way from the ground to the roof. Rats can climb up textured walls and enter cracks at the roof line.
  • Openings to the roof, including vents and chimneys. Vents should be intact with no large gaps. Chimneys should have caps to exclude rats and wildlife.
  • Openings where pipes, wires, and cables enter the home. In older holes these were often drilled large and are major access points for rats. Cover these openings with ¼ inch hardware cloth, sheet metal, or cement filler.
  • Openings in roof or eaves. At the junction of roof pitches or gables, there may be openings that allow rats to access the attic. Replace missing or broken roof tiles.
  • Underground. Norway (sewer) rats have the ability to enter the home underground or through the sewer lines. They find breaks in drain pipes caused by faulty joints, poor construction, or by tree roots. You can sometimes find their burrows in yards, under sidewalks, driveways, or under buildings.

Rats will try to return to their nest once they have been excluded and will attempt to make new access points. Continue closing access points until you are sure the rats are no longer getting inside.

A black and white line drawing of the side view of underground, showing a rat heading from a sewer line through pipes into a house
Norway (sewer) rats can enter homes from underground or through sewer lines.

 

Signs of Rodent Activity

Live rat sightings after dark are a sure sign that rats are around however there are many other signs that can help determine whether rodents are present inside:

Rub and Grease Marks

May contain: housing and building
Arrows pointing to rodent rub marks

Rats will often use the same route of travel to move between their nest and sources of food or water. This is called a ‘runway’. Over time, dirt and oils from their fur will leave a smudge or stain on walls or other surfaces. You may see these rub marks on beams or rafters, on vertical pipes, or along ledges. You may also see swing marks where rats ‘swing’ their bodies under obstacles.

 

 

Droppings

May contain: plant, seed, grain, produce, vegetable, and food

You may find rodent droppings around compost or garbage bins, near pet food bowls, or in attics. New droppings look shiny, old droppings look dusty. If you aren’t sure, clean the area and watching for new droppings. Wear gloves and spray areas down with disinfectant before cleaning in order to protect yourself from diseases.

 

 

Gnawing Damage

Rats can gnaw a small hole into a larger hole.

Rats gnaw to enlarge holes, gain access to structures or containers, to “taste” novel surfaces, or just for fun. Gnaw damage can be seen on plastic or cardboard containers, wiring, or access points to the outside. Wire damage may cause house fires. Rats have two lower incisors and most containers will show two knife-like teeth marks per bite.

 

 

 

Tracks

Rat track and mouse tracks.  Rat tracks have a longer hind foot track and a smaller front foot track, while mouse tracks look similarly sized front and back.  Both rats and mice have 5 toes on the back feet and 4 toes on the front feet.

Rats have very small tracks with four toes on the front feet and five toes on the back. The tail usually does not drag. Rats usually like to sit and eat or gnaw and do not run back and forth much so the tracks are distinct. Mouse tracks look similar but are much smaller. Mice run back and forth a lot causing the tracks to be muddled and look like a lot of overlapping dots.

 

 

Burrows or Holes

Norway rats create burrows or holes for nesting and storage. All rats may create holes to gain access to structures.

Signs of Rats Feeding

Rats sometimes drag food to a safe location to consume it, or cache for later. You may see piles of snail shells, wrappers, or vegetation in sheltered locations. Rats will also leave bite marks on fruits, vegetables, food containers, or nuts. Roof rats often gnaw the peel from citrus fruits on trees, leaving the flesh behind.

Noises

If rats get inside your house or other structure, you may hear noises – feet pattering, small thumps, squeaks, or gnawing noises - from the attic or walls, especially at night. Outdoors in the evening and morning you may hear vegetation rustling.

Odors and insects

Severe infestations may create odors from urine or droppings. If rodents die in the walls there may be a ‘dead animal’ smell as well as a large number of flies appearing indoors. Infestations may also bring with them rat fleas or mites that may bite people.

 

 

Page last reviewed: July 23, 2021

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