Mice and rats are common household pests all over the world. There are many different types of rodents, but the ones that most often cause problems are known as commensal rodents, which translates as “sharing one’s table.” In other words, these rodents live in close association with humans and depend on human habitat for food, water, and shelter. You can get rid of rodents around your home and property by: learning to identify specific species, understanding methods of prevention, and employing necessary control measures.
The three types of rodents that are typically categorized as commensal are the house mouse, the roof rat, and the Norway rat. These pests may look and behave slightly differently, but many of the same prevention and control measures can be used on all three of them. Let’s take a closer look at these pests.
The House Mouse
House Mouse By George Shuklin [CC BY-SA 1.0 (https://creativecommons.org/licenses/by-sa/1.0)], from Wikimedia Commons
The house mouse (mus musculus) is widespread and is known for multiplying quickly. These mice are small and thin, ranging from 1-2 inches for the body and head, plus a long tail that doubles the length. House mice have large ears, a pointed nose, and small eyes. They are most often light gray or brown with a lighter underside.
House mice are very common in homes. They can squeeze through very tiny holes and will nest in wall and ceiling voids, storage areas, under appliances, and many other places throughout the home. Mice tend to nibble on food regularly rather than eat big meals. They may not eat a large quantity of food, but their saliva, urine, and feces can contaminate large amounts of food. House mice are great climbers and can even climb vertically along textured walls. They can also jump a staggering 13 inches off the floor. Their normal diets consist of seeds, grains, and insects, but once indoors they also enjoy sweets, nuts, and cereals.
Signs of House Mice
The presence of house mice can be determined by various signs of activity. One of the best ways to determine what species of rodent is present is by examining the droppings. The droppings of a house mouse are rod shaped and range from ⅛ – ¼ inches long with pointed ends. House mice will gnaw holes that are approximately 1.5 inches in diameter and are clean and smooth. They will also gnaw on paper, boxes, and other things to use for nesting materials. If there are dusty areas on the floor, you may be able to see mouse tracks, but they are usually not very obvious.
The Roof Rat
Roof rats (Rattus rattus) are also known as black rats, ship rats, or white-bellied rats. Adult roof rats are much larger than mice, but young rats may often be confused for mice because they also have large ears, pointed noses, and small eyes. One way to tell rats and mice apart are by the size of their head and hind feet. Rats have proportionally larger heads and feet compared to their bodies, while mice have proportionally smaller heads and feet. The fur of a roof rat is usually smooth and dark gray or black in color. An adult roof rat is between 7-10 inches long, plus a tail that is longer than the combined length of the head and body.
Roof rats are native to tree forests in SE Asia, so they prefer moderate to warm climates and are excellent climbers. They often nest above ground in trees, attics, ceiling voids, and roof lines. They are attracted by thick vegetation, fruit trees, and areas where pets are held. They are nocturnal animals and are most active at dawn and dusk.
Signs of Roof Rats
The droppings of the roof rat are approximately .5 inches in length and are spindle shaped. This means that they are cylindrical, but taper at the end, forming points. Roof rats will tunnel through insulation and chew on wood, pipes, and electrical wires.
The Norway Rat
By AnemoneProjectors [CC BY-SA 2.0 (https://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons
Norway rats (Rattus norvegicus) are also known as sewer rats, brown rats, water rats, wharf rats, and gray rats. It is believed that they were native to northern China, but these rats have successfully made their way around the entire world and now inhabit every continent except Antarctica. Norway rats are the largest of the three commensal rodents and average about 8 inches long, plus a tail that is scale-like and shorter than the combined length of the head and body. Norway rats have small ears, small eyes, and blunt noses. Their fur varies in color, but is often brown or gray and shaggy and coarse in texture.
Norway rats are larger and more aggressive than roof rats. They tend to live in burrows along foundations, under shrubs, or among trash. They will eat nearly anything including meats, grains, small reptiles and mammals, and trash. Due to their larger size, Norway rats require more water and will drink out of toilets, sinks, and condensation on pipes. Inside a home, Norway rats typically inhabit the lower levels like crawl spaces, basements, and wall voids. They are nocturnal and feed at night.
Signs of Norway Rats
The droppings of Norway rats are much larger than those of mice. They are capsule shaped (shape of a pill) with rounded blunt ends. The droppings are shiny black and up to .75 inches in length. If you find tracks in mud or dusty areas, the hind foot marks are .75-1 inch long and you may also notice tail marks, as they drag it behind them. If you suspect activity from Norway rats, you can use unscented baby powder in the suspected area and watch for markings. Holes chewed out by Norway rats are about 2 inches in diameter with rough edges. They may also show oily rub marks from frequent comings and goings. If the population of Norway rats is large enough, you may also hear scratching or fighting sounds coming from the walls. This may indicate a particularly large infestation. Like other rodents, Norway rats gnaw on things to keep their teeth from growing too long. They will gnaw on wood, insulation, and wiring, which can cause a fire hazard. You may also notice urine stains, a musty odor, or runways where they enter and exit.
The Dangers of Rodents
According to the CDC, rodents are known carriers of at least 35 diseases worldwide that can be spread either directly or indirectly to humans. Direct contact with rodents or their urine, saliva, or feces can spread hantavirus, leptospirosis, hemorrhagic fever, and many other diseases. Indirect contact is when ticks, mites, or fleas that have fed on rodents spread diseases to humans. Typhus, Rocky Mountain Spotted Fever, and Lyme disease are some of these indirect diseases. Rodent borne diseases can have serious consequences for the individuals affected.
Not only do rodents carry harmful diseases, but they can cause damage within homes. Rodents can contaminate large quantities of food, tunnel through insulation, create holes in drywall, and chew up wood and wires. The danger of a house fire becomes a real possibility when rodents attack the wiring, so it is vital to keep the population under control.
Rodent Prevention Methods
There are many things that can be done to prevent rodents from causing problems around your home. There are three basic methods of prevention: removal of harborages, exclusion, and sanitation.
Removal of Harborages
- Cut back trees, weeds, and other overgrown vegetation
- Store firewood off the ground
- Use rock or concrete as a border along the edge of the home
- Declutter your yard and home
- Trim tree limbs to be at least 6 feet away from the home and roof
- Don’t store boxes on the floor
- Seal small exterior cracks with latex caulking
- Use wire mesh and expandable spray foam to seal larger cracks and gaps, especially around where pipes or electrical wires enter the home
- Cover vents, chimneys, and other open areas with mesh
- Ensure that garage doors close securely
- Make sure doors and windows fit tightly and have weather stripping or door sweeps attached
- Do not leave pet food outside overnight
- Make sure that trash cans and garbage dumpsters have lids and are sealed
- Do not leave food out on the counters
- Seal food in airtight containers or in the refrigerator
- Wipe counters regularly
- Vacuum and sweep floors daily
- Ensure there are no leaky pipes or faucets
- Wipe up any water that may puddle on counters or floors
- Ensure proper drainage around the yard
- Clean gutters
- Clean up dog droppings from the lawn
- Dispose of old fruit or vegetables that may be on the lawn or in the garden
Sometimes prevention methods do not work perfectly, and you may find yourself with rodents in and around your home. When this happens, the use of both traps and baits is recommended to control the population.
One of the reasons it is important to be able to identify whether you have rats or mice is so that you can choose an appropriately sized trap. If you are dealing with rats, the trap will need to be much larger than if you have mice. There are a wide variety of traps that can be used, but snap traps and glue traps are some of the most common. For mice, place several traps in areas where you have noticed activity. Place these traps 2-3 feet apart. When setting traps, place them perpendicular to the wall at a right angle with the trigger end nearly touching the wall. Bait the traps with peanut butter, hazelnut spread, fruit, or grains. If you are trapping rats, place several traps 15-20 feet apart in well-established runways. You can place rat traps parallel to the wall back to back with the trigger ends facing out so that they will be tripped no matter which direction the rat is coming from. Check out PF Harris’ full line of rat and mouse traps.
Poison baits for mice and rats are called rodenticides. The safest way to use baits is in tamper-resistant bait stations. Even with bait stations, it is still important to keep them out of reach of pets and children. Bait stations can be placed indoors in areas where rodent activity has been seen. The rodents will feed on the bait and then die. You should maintain a constant supply of fresh bait for approximately 15 days or until you have noticed a stop in the rodent activity. It is important to clean up any dead rodents or used bait stations using appropriate safety precautions, especially the use of gloves.
If you are in need of help with rodents, you can trust PF Harris for safe, effective products. We are the oldest EPA registered pest brand in America. We specialize in helping with DIY pest control. Visit us online or in stores today.