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Rats & Mice

Biology & Diseases


We all agree commensal rodents are good for nothing.  In fact, the word “commensal” means these rodents live off humans without returning anything of worth.  The Norway rat (Rattus norvegicus) and house mouse (Mus musculus) are the prevailing rodent species found in Indiana.

The rat’s tail is shorter than the head and body.  The ears are close to the body and do not cover the eyes when bent forward.  The eyes are small and the nose and muzzle are blunt.

Rats usually live in underground burrows, but will inhabit wall voids.  They feed on garbage, meat scraps, cereal grains, vegetables, and cat and dog food.  Rats will dig undigested food out of cat and dog feces and eat it.

Mice tail size equals the length of the body, which averages about 4 inches.  The ears are big and nose is pointed.  Mice live for about year.

Mice fear rats, so you may have one or the other; not both.  Rats will eat mice.


  • Droppings and urine trails left wherever they travel, especially in corners. Rat droppings look like little footballs. Mouse droppings look like pieces of rice
  • Dark smears and rub marks on baseboards as they move throughout their territories
  • Footprints and tail drags in dusty areas
  • Gnaw marks on wooden surfaces, especially door corners
  • A distinctive, musky odor
  • House pets may become agitated because they hear gnawing, digging, running and fighting


Rats and their fleas are capable of transmitting a variety of human diseases.  Mice are also capable of transmitting disease, while also contributing to asthma conditions.

  • Asthma is triggered in humans by many things, rodent hair and urine included.
  • Hantavirus is carried and transmitted by the deer mouse through its urine, droppings, and saliva.
  • Human Lymphocytic Choriomeningitis is a rodent-borne viral infectious disease that causes serious neurological problems.  It is primarily carried by the house mouse, but hamsters in contact with wild mice at a pet store can also carry the disease.
  • Leptospirosis (Weil’s disease) is contracted through water or food contaminated with the urine of infected rats.
  • Plague, a disease carried by a bacterium called Yersinia pestis, is known to exist in the western United States, South America, Africa and Southeast Asia.  Humans are infected by the bite of the Oriental rat flea.
  • Rat-bite Fever is rare in the United States.  It is caused by the bite of an infected rat.
  • Salmonellosis is a bacterial food-borne illness.  It is transmitted when rodents contaminate food or working surfaces where food is prepared.
  • Typhus is transmitted to humans by infected rat fleas, usually Xenopsylla cheopis, the Oriental rat flea.  The flea will defecate while sucking blood and contaminate the bite site.

Controlling rats and mice is more than just plugging entry holes, setting traps, and putting out poison bait.  The best control is to take away available food, water, and shelter.


The first step is a cleanup program.  Rats and mice find shelter under old lumber piles and stacked firewood (should be stored 18 inches off the ground), piles of old papers, boxes, bags, broken-down sheds, trash dumps, high weeds and abandoned vehicles.  All such areas must be eliminated or corrected.  Any control program without environmental improvement will be ineffective.  These rodents can rapidly restore their original population levels due to their high birth rate.

Interior sanitation also needs to occur.  Once rats or mice are in your house, their population levels will increase if there is available food and water.  Remember rats will eat about anything.  If there is a cockroach problem, rats or mice can feed on the insects.  Clean up food crumbs and fix water leaks.


This means stopping the movement of rats and mice into buildings or other areas where they are not wanted.  Rats can squeeze through a hole the size of a quarter; mice can move through a hole the size of a dime.  Favorite entranceways are poorly fitting doors and windows, holes around lead-in pipes and wires, dryer vents, joints between building foundations and walls, cracked siding, and unscreened doorways.  All such openings should be closed using sheet metal, hardware cloth or cement.  Doors and windows should be adjusted to close tightly.  It is also important to have tight-fitting covers on floor drains.


There are five methods generally used for population reduction:  trapping, glue boards, burrow fumigation, tracking powders, and oral toxicants.

  • Trapping is a practical way of removing rats and mice, especially where poisons might be hazardous and where odors from dead animals would be objectionable.  The most effective and versatile trap is the wooden-based snap trap.
  • Glue boards involve the use of a non-toxic sticky substance on heavy squares of cardboard.  They are placed in active runways.  When the animals become trapped, they are killed and the board is thrown in the trash.  These are well-suited for restaurants and food-handling establishments.
  • There are several chemicals federally-registered for use as fumigants against commensal rodents.  They should never be used where there is danger of people or non-target animals coming in contact with the gas.  For that reason, most fumigants can only be used by professional pest control operators.
  • A tracking powder is effective when food is plentiful.  They work by having the rodent come into contact with it; then the rat or mouse cleans itself; and, the rodent ingests the poison.  Tracking powders should never be used in areas where there is any danger of the powder coming in contact with food or surfaces where food is prepared.
  • There are two general types of oral poisons:  single and multiple doses.  Killing success with single dose poisons depends on the animal consuming a lethal amount at one meal.  Multiple dose poisons have a lower concentration of toxicant.  They rely on several days of consecutive feeding.  No toxic bait is 100% effective.  Trapping is necessary for every last rodent to be removed.  Also, placement of bait inside a structure can cause several problems.  Children or pets may eat the bait and have adverse reactions.  Rats and mice that eat the bait may die in a wall void or other unreachable areas and produce a decomposing odor.

Cleaning Up Rodent Droppings and Urine

If there is a large amount of droppings and urine to clean up, take great care because rodent-borne disease could be present.

  • Open windows for ventilation.
  • Wear gloves.
  • If a large amount of droppings and urine are present, wear an N-95 respirator mask.
  • Spray the droppings and urine with a disinfectant or bleach solution (1 part bleach per 10 parts water).
  • Wipe with paper towels.  Throw the towels into the trash.
  • Spray the disinfectant or bleach solution on to the surface and wipe or mop.
  • CDC Guidelines on Cleaning

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