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Environmental Health

Vector Control: Rodent Abatement Program

As of January 2009, with the implementation of Ordinance 159-08, our Rodent Abatement efforts will be both a proactive and complaint-based program to identify and control rat and mice infestations in the City and County of San Francisco.

Rodent Types

The three important urban rodents are Norway rats, Roof rats and House mice . The Norway rat, also called the brown, wharf or sewer rat, can be found virtually everywhere humans live. They are attracted to areas that provide a wealth of hiding places and easy access to food. The roof rat, an agile climber, is more at home in the city, with its wires and tall buildings. House mice can establish long-term residence in homes and offices. They are well adapted to life without a steady water supply, and are able to survive long periods on cereals and food scraps.

What to Look For

The sight of a rat running across an open space is often the first sign of an infestation. However, because rodents are secretive and are active at night, more detailed inspection of the sites is required to confirm actual rodent infestation.

  • Look for scattered rat droppings near common pathways, feeding locations, or shelter.
  • Look for scratches and sharp gnawing marks on the bottoms and corners of doors, on ledges, in corners of walls, and on stored material.
  • Look for dark, greasy rub marks caused by the rat?s fur oil coming in repeated contact with painted surfaces or wooden beams.
  • Check for tracks and tail draglines on dusty surfaces indoors and in loose soil and mud outdoors.

Ridding an Area of Rodents

Prevention is by far the best way to deal with rodents, because once they infest an area, they must be killed, and there is no fool-proof method that produces a quick, painless death. Here are some of the non- and less-toxic approaches to rodent destruction. All have their plusses and minuses:

Live Rodent Trapping
Live traps can be used to catch rats and mice. Once caught, the rodent can either be killed or released. Relatively humane ways of disposing of a live rodent are by drowning or freezing: To drown, confine the rodent inside a heavy-duty paper bag, then submerge the bag in a bucket of water held down with a heavy object such as a brick. To freeze, place the bag inside a larger plastic garbage bag, seal it and place it in the freezer for a couple of hours. The rodent will lose consciousness before it freezes. IPM practitioners do not recommended the release of rodents in fields or vacant lots since they find their way back again.

Spring-Loaded Traps
When rodents are instantly killed with a trap, this is possibly the most humane method of control. Unfortunately, they are not always killed outright, or at all. If using a trap, use expanded-trigger traps whenever possible. Information on snap traps.

Chemical-Control Options
Use poison baits only when trapping and rodent-proofing have failed to solve the problem. A word of caution when using poison baits: Rodents poisoned by baits will take several days to die. There is a chance that a mouse or a rat will die within walls and becomes inaccessible to remove. A decaying rodent can create foul odors and presents a health hazard.