In most cases of rodent infestation, the pest animals can be controlled without having to resort to the use of poisons. The practices of good sanitation and exclusion will prevent most problems. If rodents do find their way indoors, small populations can be easily eliminated with various nontoxic methods. Rodenticides (rodent poisons) need only be used in cases of large or inaccessible infestations. The trapping of rodent pests is often preferable to the use of poisons. Traps prevent rodents from dying in inaccessible places and causing an odor problem. There is no chance of an accidental poisoning or secondary poisoning of nontarget wildlife, pets, or children with the use of traps. Secondary poisoning of pets or wildlife can result from eating poisoned rodents. Traps can be used in situations where poisons are not allowed, such as in food handling establishments.
The roof rat or black rat is the most common rat encountered in buildings. These rats are excellent climbers and often nest in attics, wall voids, hollow trees, and in palm thatch. They prefer to travel off the ground and enter houses from nearby trees or along power lines. Roof rats prefer fruit (they are sometimes called citrus rats), but will eat any type of human, pet, or livestock food. Peanut butter, pieces of fruit or nut meats are the best baits. Rats are usually fearful of new items in their environment and avoid them for several days. This means that traps should be left in place for at least one week before they are moved to a new location. The presence of roof rats can be determined by gnawing damage, the presence of droppings, sightings, sounds of scratching, squeaking, or gnawing in walls or ceilings, and characteristic dark, greasy rub marks along frequented paths along walls and on rafters. Rats have large home ranges and may travel over 50 yard to reach food or water. Concentrating traps along rat runways or favorite routes of travel is most effective.
Rats occurring in sewers are generally Norway rats. These rats are strong burrowers, but can also climb well. They are excellent swimmers and can swim under water for up to 30 seconds and can enter houses by coming up toilet pipes. These rats usually dig burrows along building foundations and under debris piles. They have a strong preference for meat and fish, but will do well on any type of human or pet food. Raw or cooked meat and fish, especially sardines, are excellent baits, but peanut butter also works well. Like the roof rat, the Norway rat is cautious of new objects and has a very large home range, over 50 yards in radius. The Norway rat is very aggressive and will drive roof rats out of an area. However, both species of rats can be found in the same building, with roof rats in the attic and Norway rats in the basement.
Proper sanitation will do a great deal to control rodent pests. All animals have three requirements for life; food, water, and cover. Removal of any one will force an animal to leave. The removal of debris such as, piles of waste lumber or trash, used feed sacks, abandoned large appliances, and trimming the dead fronds from palm trees will substantially reduce the harborages for rodent pests. Stacked firewood stored for long periods provides good harborage for all three commensal rodents. Storage of pet food and seeds, such as wild bird seed, in rodent proof containers of glass or metal, will eliminate these food sources. Collect and remove fallen fruit from backyard trees and orchards. Keeping lids on trash cans and closing dumpsters at night will also make an area less attractive to rats and mice. The drainage holes in dumpsters should be covered with hardware cloth to keep rodents out.
Exclusion is also called rodent-proofing.
This involves making your home a fortress that rodents can not breach. Rodents can squeeze through any opening that their head can fit through. That is a 1/4 inch opening for mice and a 1/2 inch opening for young rats. Young rats and mice are the dispersing individuals, so these are the ones most likely to invade new areas, like your home. Any opening that a pencil can fit through will admit a mouse. Below is a list of recommended materials for excluding rats and mice.
Traps should be placed where rodents are likely to be. Rodents are creatures of habit and prefer to follow the same runways they usually use. It is important to identify these runways and place traps there. Runways can be identified by sprinkling a fine layer of flour or baby powder in suspected areas and looking for tracks. This is a safe diagnostic method for determining rodent activity, but should not by confused with the use of Rodenticide Tracking Powders which require a restricted use pesticide license. Rodents often run along edges and traps should be set along walls, especially where objects such as a box or appliance will guild them into the trap. The type of bait used depends on the species of rodent pest. Roof rats prefer to travel above the ground and are easier to trap along these precarious pathways than on the ground.
Multicatch traps are designed to repeatedly catch a rodent and reset themselves for another capture. Advantages of these traps are the ability to capture several rats or mice with one setting and the scent from the captured mice entices others to the trap. The disadvantages are that the captured mice or rats are alive and must be dealt with and these traps are expensive. Methods for dealing with the captive rodents includes submerging the entire trap in a bucket of water and drowning them, using drowning attachments available for some traps, placing glue boards in the holding compartment of the trap, or finding someone with a pet snake that eats mice or rats. The release of commensal rodents outside is not a solution, since they will quickly find a way back into your home or someone else's. Trap wise rodents are also more difficult to trap than naive ones. Multicatch traps must be checked on a regular basis like any other trap to prevent the capture rodents from starving or dying of thirst and creating an odor problem. Available multicatch traps include the Kness "Ketch-All" Automatic Mouse Trap, the Victor Tin Cat Repeating Mouse Trap, and the "Rat Katcher" (previously the "Katch-All") Repeating Rat Trap.
Single catch live traps are rodent sized cage traps of various styles. These traps capture the rat or mouse alive and unharmed, but again you have to deal with the captured rodent. The native rodents, cotton mice and eastern wood rat, that occasionally invade rural and suburban homes can be released back in the woods with little chance of them returning indoors. They can be recognized by their fine brown fur, white belly, large eyes, and very large ears. Commensal rodents should not be released because they will return to your home or someone else's. Rodents caught in these traps are best dispatched by submerging the entire trap in a bucket of water. These traps should be used in areas known to be occupied by endangered native rodent species, for example: on barrier islands and the Florida Keys, to confirm the species of invading rodent and prevent the accidental killing of an endangered species. These traps should be placed against walls or in runways. The most effective bait for mice with this type of trap is rolled oats (uncooked oatmeal) sprinkled inside the trap with a fine trail leading out. Rat sized live traps are produced by Havahart, Kness Mfg., Mustang Live-catch Traps, Safeguard Live Animal Traps, Sherman Live Traps, and Tomahawk Live Traps. Mouse sized live traps are produced by Havahart, Sherman Live Traps, Tomahawk Live Traps, and Trap-Ease Mouse Live Trap. Glue boards are used just like snap traps. While both rat and mouse sized glue boards are made, these traps are most effective against mice. Rats are often strong enough to pull themselves free from glue traps. Glue boards should not be set in wet or dusty areas because these conditions render the traps ineffective. Wet feet and fur will not stick to the glue and dust coats the glue till it is no longer sticky. These traps also should not be set where children or pets will contact them. Glue boards are not hazardous to children or pets, but the encounter will create a frustrating mess. Clean up hands with room temperature cooking oil and clean surfaces with paint thinner or mineral spirits. The best glue boards have at least a ??? to 1/4 inch layer of glue. Do not set glue boards near open flames or above carpets. Glue boards should be secured with a tack or small nail, wire, or double sided tape if they are placed on ledges, pipes, or rafters over food preparation surfaces or carpets.
Rats are strongly nocturnal, so the best hunting is at dusk and after dark. A red or amber filter over your flash light will aid you in seeing your targets without alarming them. Rodents, like most nocturnal mammals do not see in color and do not seem to see in the red or amber wavelengths.
Ultrasonic devices will not drive rodents from your home if food, water, and shelter are available. However, ultrasonic devices may have a part to play in rodent integrated pest management. Ultrasonic devices may increase trapping effectiveness by altering the normal movement patterns of individual rodents. Traps set in the sound shadow areas will become more effective since the rodents will be concentrated in these areas. The high cost of the units must be considered against the increase in trapping effectiveness to determine if they are cost effective.
Authors: W.H. Kern, Jr. and P.G.Koehler , University of Florida
Photographs and Graphics: University of Florida
Published: March, 1998