Indoor Pests: House Mice

Introduction to mice

Rats and mice are important rodent pests entering Florida homes and warehouses for food and harborage. These rodents eat any kind of food that people eat. They also contaminate 10 times as much food as they eat, with urine, droppings and hair. They can carry at least 10 different kinds of diseases including bubonic plague, murine typhus, spirochetal jaundice, Leptospirosis, rabies, ratbite fever and bacterial food poisoning. Many times rats bite sleeping children while trying to get bits of food off them that were not washed off before bedtime. Rats and mice also start fires by gnawing matches and electrical wires in homes.

House Mice

House mice normally live outdoors in fields, occasionally migrating into structures. In houses, they live behind walls and in cabinets and furniture.

They prefer to feed on grains but usually nibble at a wide variety of foods. House mice require only 1/10 ounce of food and 1/20 ounce of water daily, but can survive on food alone if it has high moisture. Frequently house mice range 10-30 feet from harborages.

House mice are brown to gray in color with the tail as long as the body. Adults weigh about 1/2 ounce. Their droppings are 1/8 inch long and rod-shaped. House mice live about one year and reach sexual maturity in six weeks. They have five to six young per litter and up to eight litters per year.

Mice Behavior

The movement of rats and mice is usually related to food, water or harborage. Knowing where they are likely to go is important to controlling them.

Rats use any method to get to food, water or harborage. Their excellent sense of balance enables them to run on pipes, narrow ledges and utility wires. Rats, especially roof rats, will climb anything their claws will hold on to, including wires, pipes and rough walls. Because rats are excellent swimmers, they often live in sewers and occasionally enter homes through toilets.

Rats like to use regular paths or runways along walls or behind debris. To get food in the open, they will run behind things to get as close to the food as possible. They are afraid of strange objects or strange food and may avoid both.

Rats and mice are active mostly at night. Rats show greatest activity the first half of the night, if food is abundant. Mice usually are active at night both right after dark and between midnight and dawn. Both rats and mice will be active during daytime hours when food is scarce, when there is an overpopulation of rats, or when a poison has been used and the population is sick.

Rat and Mouse Signs:

Droppings and Urine

Most people first recognize rodent problems by finding droppings or urine stains in and around buildings. Rodents usually have favorite toilet areas but will void almost anywhere. Old droppings are gray, dusty and will crumble. Fresh droppings are black, shiny and puttylike. Rodents urinate while running, and streaks are characteristic. The urine glows under ultraviolet lights and glows blue-white when fresh.

Gnawed Objects

Rodents gnaw every day in order to keep their teeth short and sharp. Rats also gnaw to gain entrance or to obtain food. Teeth marks on food, building materials, wire, and edges of beams are indications of gnawing. Rodents will gnaw holes in wooden walls, pressed wood and posts. Fresh gnawing in wood is usually light-colored with sharp, splintery edges. Old gnawing is smooth and darker.


Rats habitually use the same paths or runways between harborage and food or water. Outside runways are paths two to three inches wide and appear as smooth, hard-packed trails under vegetation. Indoors, runways are usually along walls. Undisturbed cobwebs or dust indicates runways are not being used.


Along runways, dark greasy rubmarks appear from contact with the rodent's body. Rubmarks on walls appear as black smudges left by the rodent. New rubmarks are soft and will smudge. Old rubmarks are brittle and will flake when scratched. Rafters may show swing marks of roof rats.


To detect rodent activity, spread dust material like talcum powder along runways. Footmarks of rats (five-toe hind foot, four-toe front foot) or tail drag marks will show in the powder.


Usually rodent sounds are heard at night or in quiet areas. Rodents moving at night often scratch, gnaw, and fight. The young often squeak while in the nest.