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? Does that gnawing you just found mean that you have more mice or rats? Or is it from the old infestation?
Some tips for determining whether you have a current or previous infestation include:
- Droppings. New droppings are dark and moist to the touch. As droppings age, they dry out and become old and gray and will easily crumble when touched. Droppings are most likely to be found around food packages, in drawers or cupboards, under sinks, in hidden areas, and along rodent runways. Additionally, You will find the greatest number of droppings where the rodents are nesting or feeding, so inspect the area around the new-found droppings to determine if there is still an active – or new – infestation.
- Gnawing. In contrast to the droppings, newer gnaw marks will be lighter in color and become darker as they age. These will often be found on food packaging or the structure itself. One way to determine age is to compare the newly found gnaw marks 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 will have been produced by the larger teeth of rats. Thus if you had a mouse infestation, but are now seeing larger gnaw marks, you may now have rats. And vice versa.
- Odor. Cats and dogs, or rodent pets, 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 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 smell coming from hidden areas, indicating an active infestation.
- Tracks and runways. If rodents are currently active in or around your home, their runways and tracks are likely to be distinctive, becoming fainter as time passes. Tracks are runways are most easily identified 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 placing a very thin layer of flour or baby powder in the area. If rodents are active, you are likely to see their trails in this powder.
- Nesting. 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.
- Outside indicators. Rodents are attracted to piles of trash, organic waste, etc. for both food and harborage. If these are present near the home or structure, inspect them for signs of rodents. If there is no indication of rodents, it is likely that they are not coming into your home either. If you do have such piles present, eliminating them can help prevent future rodent problems.
- 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, numerous fresh droppings or gnaw marks, it is likely that the population has gotten quite large and may require professional services.
Adapted in part from publications by: