The Weather has Cooled Ushering in Rat and Mouse Season


Recently, a Contra Costa County resident recounted the story of taking her car to the mechanic for an oil change, only for the mechanic to discover a rat’s nest under the hood. After the resident’s initial surprise, the mechanic explained that he has seen this before, typically when the weather cools and rats look for warmth, which they can find on a warm engine.

Norway Rat (Rattus norvegicus)
House Mouse (Mus musculus)

A few years ago, another resident shared how much she paid to repair the damaged wiring in her car that had been caused by a rat seeking warmth in her car that then gnawed on the wiring and cables.

These stories are not unusual because rats and mice are common in Contra Costa County. The key is to take the following steps to reduce the risk of damage and disease from rats and mice on your property.

Remove Food

Rats and mice can be attracted to a yard by the availability of food. The first step to keep rats and mice from being attracted to your home is to remove potential food sources.

  • Pick up fallen fruit and nuts and harvest mature fruit and nuts from trees as soon as possible. This is especially important when the fruit is citrus or berries.
  • Store grass seed and bird seed in metal containers with tight-fitting lids.
  • Also, store pet food in metal containers with tight-fitting lids, and be sure to bring pet bowls indoors before nightfall.

Remove Shelter

Once a rat or mouse has found a source of food on a property, they are more likely to look around for shelter. After removing food options, it’s time to remove potential sources of shelter.

  • Rats and mice can live in dense vegetation, particularly types of ivy. Remove or trim dense vegetation.
  • Also, trim climbing vegetation four feet from a roof, walls, fences, utility poles, and trees.
  • Store wood and lumber piles at least 12 inches above the ground and 18 inches away from any structure.
  • Keep shed doors closed at night and install wire mesh on the base of the shed to prevent access under the shed.

When rats and mice find food or shelter they have more time on your property to look for entry into your home. Find more information here on where rats and mice commonly enter homes and what to do about it.

Reduce the Risk of Leptospirosis

Keeping rats and mice out of your home is important because they can spread bacteria and viruses through their waste products and nesting materials which can make people and pets sick. Rats and mice are known to transmit the bacterium that causes leptospirosis through contamination of water sources. “Leptospirosis is endemic in the Bay Area, and the threat it poses is real,” said Dr. Eric Barchas, DVM, Medical Director of San Bruno Pet Hospital.

Dr. Barchas explains the bacterium is spread when an infected animal urinates in or near a water source, contaminating the water source. When a rat or mouse gets into a home, it can crawl and gnaw its way into food cabinets and appliances, contaminating indoor food and water sources and putting people at risk. According to the Centers for Disease Control and Prevention (CDC), people can also be exposed to the bacterium that causes leptospirosis outdoors while engaging in activities that involve water, even wet or flooded soil because the bacterium can enter the body through the eyes, nose, mouth, or abrasions in the skin. The CDC says the majority of people who become sick experience mild flu-like symptoms; however, up to 10 percent of people who become infected can experience potentially life-threatening symptoms.

Man’s best friend can also become infected from contaminated water sources that are large or small — even a drop of water on a blade of grass can pose a risk. When a dog swims in, drinks, or steps in the water there is a risk of infection, and that infection can be serious. Leptospirosis can infect a dog’s bloodstream, liver, and kidneys, and if left untreated it can be fatal.

There is a vaccine available for dogs to reduce the risk of leptospirosis; however, there is no such vaccine for humans, making it even more important to take the steps necessary to reduce the risk of damage and disease from rats or mice now, because the weather is only going to get colder.

About Kevin

Manager of Mainframe Operations and Optimization – USS-UPI, Co-Founder and Board Member - Friends of Oakley A Community Foundation, Trustee RD 2137, Advisory Board – Opportunity Junction
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