Rats! (and mice): Know your Enemy!
Rats and mice are important rodent pests that eat any kind of food that people eat and 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 on the child that were not washed off before going to bed.
Norway Rats
Norway rats thrive in areas where garbage is not properly stored. Although Norway rats generally prefer to eat fresh meat, fish, and grain, they can survive quite well on an ounce per day of garbage or decayed food along with an ounce of water. Norway rats are burrowers and often dig in rubbish and under buildings or concrete slabs. Adults weigh 3/4 to 1 pound and reach sexual maturity in 3-5 months. They have 8-12 young per litter and up to 7 litters per year.
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, surviving on food alone if it has high moisture. Adults weigh about 1/2 ounce live about 1 year and reach sexual maturity in 6 weeks. They have 5-6 young per litter and up to 8 litters per year.
Important Rat 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. 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 frequently gnaw on their surroundings. Their teeth grow 4½ to 5½ inches per year and only gnawing keeps them short and sharp.
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.
Recognizing Rat and Mouse Signs
Since rats and mice are active at night and are rarely seen during the day, it is necessary to recognize signs of their activity.
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 the 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. They 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.
Runways - Rats habitually use the same paths or runways between harborage and food or water. Outside runways are paths 2-3 inches wide and appear as smooth, hardpacked trails under vegetation. Indoors, runways are usually found along walls. Undisturbed cobwebs or dust indicates runways are not being used.
Rubmarks - 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.
Tracks - To detect rodent activity, spread dust material like talcum powder along runways. Footmarks of rats (5-toe hind foot, 4-toe front foot) or tail drag marks will show in the powder.
Burrows - Norway rats burrow for nesting and harborage. Burrows are usually found in earth banks, along walls, under rubbish and concrete slabs. Freshly dug dirt scattered in front of 3-inch openings with runways leading to the openings is characteristic. Burrows usually are 18 inches deep in most soils. Slick, hardpacked runways indicate an old established colony.
Sound - 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.