While the presence of rats and mice is nothing new in homes, sheds, barns and other structures, some areas of Texas are experiencing greatly increased rodent activity, leading residents to ask for advice on how to control the furry varmints.
Rachel Bauer, Texas A&M AgriLife Extension Service agent for agriculture and natural resources for Bastrop County, said Bastrop and surrounding counties have seen their mouse and rat population explode.
"Some homeowners are being invaded by mice and field rats which are thriving in the burned-out areas recovering from the wildfires, in part because there are very few predators," Bauer said. "And with the regrowth of vegetation, the rats and mice have had an ample food source and are reproducing quickly."
Bauer said she has received reports of rats chewing on wiring in and around homes, as well as in cars parked both outdoors and inside garages.
"Last fall was an exceptionally wet season in this area of Texas," said Jerry Falke, wildlife damage management biologist for AgriLife Extension's Texas Wildlife Services who is based in the Bastrop area. "The increase in late-season grass and seed was a major factor in greater native rodent activity, and the resulting population led to increased migration into residences, storage buildings, shops and other indoor locations in wintertime."
Falke said there was increased activity particularly in Bastrop, Lee, and Brazos counties, as well as Fayette County.
"I'd say in general that certain geographic regions of Texas have had increased rat and mouse activity this year, particularly the south central and southeastern part of the state to the east of the I-35 corridor," said Linda Tschirhart-Hejl, a Wildlife Services biologist based in Bryan.
Tschirhart-Hejl said other parts of the state that regularly see greater-than-average activity from rats and mice are urban areas such as Houston, Dallas, San Antonio and El Paso, though this activity usually comes from the "commensal" or non-native species that typically infest the more metropolitan areas of the U.S.
"Rats and mice eat and contaminate human, pet and livestock foods," said Bruce Leland, assistant director for Wildlife Services, San Antonio. "They also destroy property by chewing wires, which may cause fires, as well as gnaw pipes, chew water hoses and damage wood doors, floors, walls, clothing and furniture. They also carry diseases harmful to humans and domestic animals."
While neither AgriLife Extension nor Wildlife Services provide direct assistance to homeowners with rodent control, they do provide research-based, objective information and advice on how to better manage these persistent pests.
Bauer said as a possible means of control, she has suggested that, based on their situation, some people consider getting a cat or dog that has been bred or trained to be a "mouser," but also noted "there are a variety of other means of rodent control from traps to baits to exclusion."
"An integrated approach to rodent management is the best," Leland said. "A program using rodenticides and traps, removal of shelter, removal of food and water, and rat-proofing is most effective," he said.
For those who prefer to use rodenticides, many are available – most of which are anticoagulants, causing death by internal bleeding, Leland said.
"Rodenticides can be purchased in ready-to-use forms at farm and ranch supply stores, nurseries or grocery stores, he said. "They are usually formulated as cereal grains, pellets, all-weather blocks, tracking powders or water soluble formulations. Anticoagulant rodenticides are available in either single dose or multiple dose baits. Rats and mice normally die anywhere from 3 to 10 days after feeding on the baits."
Leland noted, however, that most or all anticoagulant rodenticides are registered for the control of commensal rodents only and should be used in strict accordance with their labeling.
"Be sure to place the baits in rodent travel ways or near their burrows and harborages," he said. "Do not expect rats or mice to go out of their way to find the bait. See if you can find a location where there has been a sign of activity or that you think would be in the rodents' normal line of travel."
Leland also said care should be taken in placing baits in such a way that neither people nor domestic animals have access to them.
"Containers known as bait boxes can be either purchased or constructed," he said. "Bait boxes protect baits from the weather and restrict access mainly to rodents, providing an excellent safeguard for people, pets and other animals."
He noted, however, that results from the use of baits cannot always be measured by the actual sight of dead rats and mice.
"It takes a while for baits to work, and rodents often die out of sight," he said. "So when baits are no longer being eaten, when there are no fresh droppings and when there are no live rats or mice to be seen, that usually means the baits have been effective."
Traps are just as effective as rodenticides, Leland added, but require more skill and labor.
"Rodent traps such as snap traps, cage traps and glue boards are recommended where the use of rodenticides seems inadvisable, and in places where there are few rats and mice. The best place to set traps is along travel routes where rodent sign is evident. Snap traps should be set in a location where the rodent is likely to pass over it. "
To make the trap more effective, a 2-inch by 2-inch piece of cardboard can be attached to the trigger, he said. And glue boards and cage traps should be placed parallel to the base of the wall.
"Selection of baits for trapping is also important, and bait should be fresh and changed daily."
Leland said another important part of rodent prevention is removing items that may provide shelter for them, such as woodpiles, waste piles and empty boxes and cartons.
"Materials should be stored at least 18 inches off the ground or floor, and with space between the items and the wall," he said. Store foodstuffs in rodent-proof containers such as glass or metal, and dispose of waste and garbage in tightly covered metal cans.
When it can be done at a reasonable cost, rat-proofing is recommended as the most permanent means of control, he said.
"All openings rodents can enter should be covered with resistant materials such as hardware cloth or steel wool, Leland said. "Doors should be closed when not in use, and all edges subject to gnawing should be covered with metal. Unnecessary openings should be covered with concrete or sheet metal."
He said if such efforts do not produce the desired results, then it may be necessary to contact a professional exterminator. However, he added, be sure the individual is a licensed professional with specific experience in controlling rodents.
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More information: "Managing Rats and Mice" is available online: agrilifecdn.tamu.edu/txwildlifeservices/files/2011/07/RatsMice.pdf