How to Determine the Extent of a Rodent Population

Tom Keaton

Rodents, such as mice and rats, will enter and infest pretty much any type of structure. The key to elimination is to determine where they are nesting and how many rodents you are dealing with. Learn how to determine the extent of a rodent population. .

  1. Determine where rodents have been seen. If they have been spotted in the daytime, this would generally represent a heavier infestation since rodents are nocturnal by nature.

  2. Search for droppings or feces. Full grown rats and mice will have different size droppings. Mouse dropping will average out at 1/8 to 1/4 inch in length, whereas a rat dropping will generally measure 1/4 to 1/2 inch long. Droppings will also tell you how recent the activity was in an area. If the droppings are dry and brittle, they are older. If they are shiny and soft, this is a newer dropping reflecting recent activity in an area. The amount of droppings will also be a tell tale sign of how many rodents you are dealing with. Many new droppings would represent a heavy population whereas just a few will equal a minor problem.

  3. Setting out glue traps found at a hardware store will also help you to determine the extent of the population. Place at least three to four, per room or area you are suspicious of. Use an attractant on the glue board, such as peanut butter. If you only trap one or two, you are probably dealing with a small population. If you catch numerous rodents, you can assume there is much more activity and a greater population.

  4. Look for "run marks" on walls that rodents travel along. These are dark areas along a wall or corner where rodents travel on a regular basis. The oil and dirt from their hair leave these trails. Following run marks will generally lead you to nests and also help you determine where they are getting their food and water from. If you discover extensive run marks that are taller than a couple inches, chances are high that you are dealing with numerous rats.

  5. Lay out baby powder or flour along the floors near the walls at night and try to smooth it out as much as posisble. In the morning you will be able to see any foot print and tail marks on the powder, which will help also you to determine how many rodents you may be dealing with. It may be difficult to count the prints, but it will certainly help you to know where they transit.

  6. Laying out bait without using any traps for a night or two will also help you determine the size of a population. Some cheese, pieces of hot dogs, or tuna placed on a piece of paper will work fine. If all of your bait is eaten or removed in the morning, you can suspect a larger population.

  7. Tip

    If you discover an area with a lot of droppings, put on a face mask or respirator and wear rubber gloves before removing. When cleaning droppings, it is best to wet them down first and scrape them away rather then sweep up dry particles which can become airborne. Mice will normally only travel up to 15 feet away from their nest area to find food or water whereas rats will travel much further if they need to.


    Never stick your fingers or hand into a rodent hole. If rats are living in the nest they can be very aggressive when it comes to protecting their nest. Do not confront or corner them. If you discover a large rat population, call in a professional exterminator, rather than try to solve the problem on your own.