Rats

Did you know that a group of rats is called a mischief? Rats can be destructive, disease-carrying pests. They can also make fascinating pets. This post is not about rats as pets.

​Rats as disease carriers

Rats and the fleas that feed on them are vectors of disease. The Centers For Disease Control and Prevention (CDC) lists 11 diseases directly transmitted by rodents, including plague, and 15 diseases, including typhus and hemorrhagic fever, indirectly caused by rodents. “Plague is a disease that both roof and Norway rats can carry, but in California it is more commonly associated with ground squirrels, chipmunks, and native wood rats,” according to Wikipedia. These diseases are spread through handling live or dead rats, handling food contaminated by rat urine or feces, or coming into contact with surfaces territorially marked with rat urine. If rats are present, infection is possible.

​Do you have a rat problem?

Rats can cause significant damage, transmit disease, and contaminate food. Recognizing a rat problem more often involves seeings signs than an actual rat. Rats are good swimmers and can even enter a building through the toilet. Common signs of a rat problem include:

• rat droppings around pet food, trash cans, compost piles, or behind furnishings
• nearly ripe fruit being knocked from trees and gnawed
• dogs or cats acting as though they are hearing things move in walls
• burrows or nesting materials found while working in the garden or near trash containers
• rats seen traveling along power lines (usually at dusk)
• gnawed electrical wires, doors, ledges, or window sills
• torn up insulation (used as nesting material)
• gnawed soft metal pipes (copper, lead) or plastic PVC

Brown rat (US Forest Service)

Common rat species

There are dozens of different types of rats but the two most common to California are Norway rats (Rattus norvegicus) and roof rats (Rattus rattus). They are also called brown and black rats, respectively, but these names are misleading.

​    Roof rats are medium-sized with a tail that is longer than the head and body combined. Roof rats prefer attics, trees, mature shrubs, and power lines. Roof rats eat nuts, berries, fruits, snails and slugs, avocado and citrus. A roof rat will hollow out an orange or eat the peel off of a lemon or a lime, leaving the fruit hanging on the tree in each case. A female roof rat can produce up to 40 offspring each year.

    Norway rats are larger and they prefer to burrow. They are often found in sewers, next to building foundations, and under trash containers. Norway rats prefer meat, fish, nuts, grain and some fruits. A single female can produce up to 20 young a year.

How to get rid of rats

It is far easier to control a rat population while it is small. Rat control includes monitoring, sanitation, exclusion, and trapping: 

1. Using the signs of rat infestation listed above, regularly monitor your home, garage, garden and established landscape for rats.
2. Sanitation means keeping foodstuffs and trash in sealed containers, building materials stored off the ground, and trimming shrubs to keep them at least 2 feet away from buildings.
3. Exclusion refers to rat-proofing openings for pipes, ventilation, and electrical wires with sheet metal, screen or coarse steel wool. Wood, caulk, and plastic are not rat-proof.
4. Trapping is a safe, effective method of rat population control. Using poisonous baits can put pets, children and other wildlife at risk and should not be used. Sturdy wooden rat traps can be baited with cheese, bacon, or peanut butter for the best results. Be sure to place traps where pets and children won’t get to them. Traps can be stabilized for better performance by screwing or wiring them to a heavier surface, such as a plank or pipe. Traps should be checked daily. Wear plastic gloves and dispose of dead rats in sealed plastic bags in the trash.