Minnesota Wild Animal Management | Mice and Rats

May 1, 2012

MN Mice and Rats Control

Part 4 of 5

Rats have voracious appetites. A rat can eat a third of its body weight each day. The rat is a true omnivore. It will eat anything, including soap, leather, furs, candy, milk, meat, vegetables, poultry, eggs, grain, seeds, fruit, nuts, snails and other rodents. Rats will catch fish, and they readily eat carrion. Near homes, rats thrive on pet food, birdseed, grass seed, garbage, dog feces, and the uneaten or spoiled food we discard. While rats will eat nearly anything, they prefer grain, livestock feed, and meat. Unlike the mouse, which nibbles a little at a time, rats will fill up at one sitting, if possible. Rats will hoard and cache food, which can result in insect infestations. Like mice, rats will live in freezers, feeding only on frozen food. Rats eat so much that one rat can leave behind 25,000 droppings per year. The rat’s main constraint is that it cannot go long without water unless its diet supplies enough. Rats need up to one ounce of water every day.

The number and behavior of rats change throughout the year. Many rats die during winter, as outdoor foods become hard to find. Breeding in winter is comparatively low, so rat populations are at their lowest. A mild winter means fewer rats will die of natural causes, so more can be expected in the spring. But if rats are controlled in winter, fewer will be available to resume the breeding cycle in spring. Heavy breeding begins in March when the weather turns warmer. Spring rains spur vegetation which provides cover and additional food. So rats are more abundant in late spring. Young rats have to seek food and new nests. In summer, food and vegetation are abundant, so rats continue breeding. Breeding peaks in early September as temperatures begin to fall. Sources of food and shelter start to diminish in fall, so rats look for shelter inside buildings and homes.

Getting rid of rats is difficult. Capturing or poisoning a few rats in the neighborhood makes little impact. To defeat them, a community has to cooperate in capturing or killing them, at the same time starving them, denying them shelter, and cutting off their sources of water. Denied a source of food, rats will turn to killing and eating each other, which further reduces the infestation.

Recognizing a Rodent Infestation

There are definite indicators of rodent activity:

  • Droppings – Usually, the first clue of a serious rodent problem is their droppings on the kitchen counter, in kitchen drawers and cabinets, or in the pantry. Look for mouse droppings in utility closets, attics, garages and basements. Mouse droppings are smooth with pointed ends, and are 1/8-inch to 1/4-inch long. Rat droppings are pellet-shaped, blunt at both ends, about the size of an olive pit, and shiny black. They soon fade to gray-white. Droppings are randomly scattered, but normally close to rodent runways, feeding areas, or near shelter.
  • Tracks – Rodent tracks can be observed in mud, dust or bare dirt. Often, rodent tails also leave a mark. In the house, mouse tracks can be seen on dusty surfaces. You can also check for mouse tracks by dusting suspected areas with a light coating of unscented talcum powder or chalk dust. Wait a day and then shine a flashlight across the area. If there are small tracks in the powder, mice have been there.
  • Gnawing – Rats must chew continuously to wear down their incisor teeth. Look for holes in walls or ceilings, and trails in crawl spaces, behind or under cupboards, counters, bathtubs, shower stalls, or near hot water heaters or furnaces.
  • Burrows – Burrows can be found along ditches, walls, or fences, and under buildings, rubbish, low vegetation, woodpiles or concrete slabs.
  • Runways – Rats follow the same routes as they make their rounds foraging for food each night. In doing so, they leave 2-inch wide runways in the dirt or grass, usually next to buildings or fences.
  • Grease marks – Greasy rub marks are caused by a rat’s oily fur repeatedly coming in contact with walls or entrance holes.
  • Urine stains – Urine stains are more easily observable under a black light.
  • Nests – Mouse nests can be found in utility closets, attics, garages, and basements. They are usually made of cloth or shredded paper, lined with finely shredded material. Rat nests look like a loosely woven ball 4-6 inches in diameter.
  • Partially eaten food – Mice leave behind partially eaten food. While rats eat most of the food they find, even they leave telltale signs, like shells or other inedible.
  • Live or dead rodents – People usually see mice only when they have been sitting stock still, such as when reading or watching television. Rats are nocturnal, but in areas having large rat populations some low ranked rats will forage during the day, because they have been denied access to food at night. If you see rats during the day, it is a sign of a substantial infestation.
  • Sounds – While you may not be able to see them, you can probably hear rodents moving after dark. If your pet paws at a wall or cabinet it may be trying to get at a lurking rodent.
  • Odors – Often you can smell rodent urine or their musky odor, especially in a poorly ventilated room.

Keep Rodents Outdoors

The best way to control rodents is to keep them out of the home in the first place. Since rodents like to hide in vegetation, your first line of defense is to trim the vegetation close to your home. Clean yards deny rodents the food and shelter they need for breeding, and they restrict a young rodent’s ability to move in. Piles of grass clippings or tree trimmings make ideal rodent harborages, so properly store and dispose of these materials. Try to leave a couple of feet of clear space between your house and any vegetation. Rodents also like to hide under woodpiles or lumber; in abandoned cars, appliances and furniture; and under trashcans. So remove and properly dispose of all junk. Store any lumber or wood on racks at least 6-inches off the ground, and away from the house exterior. Store your trash and garbage cans on racks too, or else on a concrete pad.

Check your house perimeter annually in late summer or early fall to assure there are no gaps that could be used for entry. Remember that a pencil-sized opening is sufficient for mouse entry. Pay special attention to pipes, wiring, conduits, cables, doors, and windows. Even where buried utility piping enters, the foundation must be effectively sealed. At night, have someone shine a light along the interior of your basement or crawl space walls while you circle the perimeter of the house on the outside. Potential entrance holes or other flaws you may not be aware of will show up under the light. Close any openings found, using sheet metal, hardware cloth, or wire mesh. Pieces of tin cut from coffee cans make great patches. Caulking will not do the job. Screen necessary openings, like fans and chimneys with ¼-inch wire mesh. Wire mesh greater than ¼-inch won’t work. Replace missing bricks. Fill in any burrows under the foundation with concrete.

Attached garages are serious weak points, because garage doors rarely fit as closely as other doors. Once a rodent has made it into an attached garage, the rest of the house is easy pickings. Therefore, to make the garage less attractive, store your trash and garbage somewhere else. But if you must store it there, be especially careful to use containers in good condition with tight-fitting lids. Never leave plastic trash bags in an attached garage. Again, shine a light along the perimeter of your garage door at night to see if it offers easy entry. Check the doors of attached garages more often than once a year.

Windows and exterior doors should fit properly, be weather-stripped, and be kept closed when not in use. There should be no holes in screen doors. Screens are easy to patch. All window and door edges subject to gnawing should be covered with metal.

Even water puddles will give rodents all the water they need to drink. So all leaks must be fixed, and all ruts and depressional areas must be drained or filled in. Keep all guttering clean so water doesn’t stand. Make sure your window air conditioner isn’t creating a puddle. Cover swimming pools and hot tubs. Drain birdbaths and ornamental ponds. Water hoses are notorious for leaking at the connections; so when you’re finished using the hose shut the water off at the spigot, rather than at the hose nozzle. Cease lawn sprinkling for the duration of the infestation.

Outside food sources that attract rodents include garbage, dog and cat food, dog feces, birdseed, and fruits or berries that have fallen to the ground. Take away their sources of food outside, and rodents will look for another neighborhood to live. Pick up fruit and vegetables in your yard. A honeycomb can feed hundreds of mice all winter, so carefully remove any beehives in the immediate area. Birds are messy eaters, which is especially helpful to rodents. So quit feeding the birds for the duration of the infestation. If you’re feeding the squirrels; you’re also feeding rodents. If at all possible, feed your pets indoors. If you must feed your pets outside, remove their food 30 minutes after serving. Otherwise, whatever you’re pet doesn’t eat, rodents will. Since rats are nocturnal, feed your outdoor pet well before dark.

Store your garbage in containers preferably made of metal, with tight fitting lids. Never leave plastic trash bags outside. Turn compost piles regularly and don’t compost meat, bones, dairy waste, fats, or oils. Remove dog feces from the yard daily.

Part 4 of 5 Continued May 5, 2012

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