You open the cabinet door and you see them—tiny black droppings on the shelf next to the package of Bisquick, or gnaw marks on the edge of the Cheerios box. Perhaps there is a little pile of shredded cardboard next to the edge of another package, just sitting there. A little whiff of a musky odor wafts out when the door opens wide. You know it—there is a culprit on the loose who is sharing your living space, and he must be dealt with swiftly and surely. Why? Because you know that letting this one stick around always leads to more.
Of course we're talking about those very adaptable little rodents called house mice. In last month's column, I wrote about the general biology, reproduction and behavior of the species. We know these animals are mainly nocturnal, so they are not likely to be running around in plain sight during the daylight hours, although they may venture out during quiet times. How then do we know when we have a problem?
Because they prefer to live inside manmade structures where food and nest spaces are plentiful, mice often occupy single-family homes, apartment buildings, commercial establishments, barns, granaries, and sheds. Observing mice in the daytime can happen in some locations (generally those that are not frequented by human activity), but in our homes we may never see them. The only sign of mouse occupancy may be evidence of gnawed packages or tiny black droppings along runways, on shelves or floors, behind appliances, or on counter tops. Or we may come across piles of nesting materials in secluded areas like drawers and pantries, or in storage areas, basements and garages. These nests are constructed of shredded materials such as paper, cardboard, fabric, or other similar fibrous sources, and generally have the appearance of a "ball" of material loosely woven together, usually 4-6 inches in diameter. A musky odor (produced by the mouse's anal glands) may be noticed in these areas, a sure sign of house mouse infestation.
Tracks, including footprints or tail marks, may sometimes be noticed on dusty surfaces. Gnawing evidence may be visible on doors, ledges, in corners, on stored materials or on other surfaces. Mice keep their paired incisor teeth (which grow continuously) worn down by gnawing on things. Thus we may run across fresh accumulations of wood or paper shavings, insulation, and other like materials which indicate active infestations.
Sounds from gnawing, running across floors or the upper surface of ceilings, climbing in the walls, or even squeaking are common when house mice are present. Visual sightings are possible even in the daylight hours (though not common), and mice can often be seen after dark if we observe quietly and with the aid of a flashlight.
Determining the extent of a house mouse problem is not always an easy task. When looking for mice, search the premises thoroughly. In structures, these searches should include basements, attics, in crawl spaces, around foundations, in cupboards, drawers, pantry shelves, behind appliances, and around stored materials. A simple way to detect the presence of mice is to sprinkle tracking-dust patches of white flour or talc in a location and then checking for tracks or droppings after 24 hours. (This can also be done at 20 to 30 foot intervals throughout a barn, shed, or commercial structure, and can be a helpful indicator of relative size and distribution of the mouse population.) Placing an inexpensive white paper plate in a suspected location in our homes is fast and easy, and checking it later for droppings will let us know that they're around.
So we have mice, now what do we do about them? Since house mice are not protected by law, they may be controlled using any pesticide registered by federal or state authorities for this purpose. Or they may be controlled by use of mechanical methods such as snap traps. Live traps are also available for those who prefer a "catch and release" outcome. Trapping is the preferred method where poisons seem inadvisable, such as in our homes where pets and children are present, and where only a few mice inhabit an area. While it requires more labor than simply putting out rodenticides, trapping does have several advantages: (1) it does not rely on potentially hazardous poisons; (2) it allows for prompt disposal of the mice, thereby eliminating odor problems from unfound decomposing carcasses; and (3) it permits the user to view his or her success (however unpleasant that may be).
The simple, old-fashioned, inexpensive, wood-based snap trap has been around for years and remains one of the most effective ways to rid our homes of these little varmints. (Other effective snap traps are available that also work well, found in just about any grocery or hardware store.) These should be baited with a small piece of bacon, cheese, nutmeat, dried fruit, or even marshmallow in the bait receptacle. I have actually found peanut butter to be very effective also. Test the trap first to be certain it has a "hair trigger", because if it doesn't snap quickly to the slightest touch, the mouse can lick the peanut butter clean or eat the bait and never set it off. Place a few traps close to walls, behind objects, in dark places, or wherever evidence of mouse activity has been seen. Use enough traps to make the campaign short and decisive. Mice seldom venture far from their food and shelter supply, so placing several no more than 6 feet apart where mice are active should do the trick. Continuing to reset the trap after successfully trapping a mouse is always a good idea, as there are usually more where that came from. Seal pathways used to enter buildings, keep garbage in secured bins, clean up pet food dishes, etc., to create a mouse-unfriendly environment.
Of course, one can always get a cat. Some cats (and even dogs) will catch and kill mice, but there are few situations in which they will do so sufficiently to control rodent populations. As for our old cat, Betty, the question remains from last month's column: Did she eventually apprehend the mouse that she discovered in our kitchen and thus earn her keep? The answer is no--and yes. The mouse never came out from behind the dishwasher into her waiting paws (after all, they're not stupid!), but I did trap it eventually with an old-fashioned snap trap and peanut butter. I have to give her credit though--she did let me know that there was a mouse in the house before I had any idea that one was around. Hmm--I guess we'll keep her.