What are common signs of roof rat activity?
Visual sightings on power lines, trees, bushes, patios, etc.
Hollowed out citrus and other fruit
Noises in the attic and walls
Gnawing sounds and gnaw marks around roof eaves
Damage to plastics and coverings on electrical wires
How to handle dead rats, rat droppings, and nesting areas [Taken from Marin/Sonoma Mosquito and Vector Control District handout]
Use rubber gloves.
Ventilate the affected area the night before cleanup by opening doors and windows.
Spray dead rats, droppings, nests and surrounding areas with a 10% bleach solution (one part bleach and 9 parts water). Allow at least 15 minutes of contact time before removal.
Clean the affected area with paper towels or a mop. DO NOT SWEEP OR VACUUM. Double bag both the disinfectant-soaked rat and cleanup materials securely in plastic bags and seal. Dispose in city trash containers.
Before removing gloves, wash in disinfectant, then soap and water. Dispose of gloves with other household waste. Thoroughly wash hands with soap and water.
Where have roof rats been found?
In swimming pools, laundry rooms, attics, garages and patios. They’ve been seen on power lines in the alleys. Roof rats spend 90% of their life 4 feet or more off the ground.
When do they travel?
During twilight and nighttime hours in a territory 200 to 300 feet from their daytime nesting locations. They thrive in cool weather and are most active from November through May.
How do they travel?
Roof rats are strongly arboreal and travel along power lines to trees, oleanders, vines and roofs. They can climb up brick walls and other rough surfaces. They can jump 2 feet straight up and 4 feet horizontally (double the horizontal distance if they are jumping from a height). Bear in mind that ground covers and compost bins also provide safe travel routes and nests.
How do they enter homes?
They enter homes and garden sheds through any opening larger than a nickel. They follow pipes down from the attic, gnaw through drywall and enter the kitchen or base sink cabinets. They chew through wood, plastic, aluminum siding, sheet rock and soft metals.
These rodents are fond of attics because they provide a safe refuge, a nesting place for their young and routes into the home below.
What do they eat and drink?
They love to eat citrus fruit (because it serves as both a food and water source) and other fruit (pomegranates, figs, etc.), nuts, seeds and stored grains, and vegetables in your garden. They also eat insects, lizards, tree bark, soap, paper, hides, and beeswax.
Bird seed (both in feeders and stored in bags) and dog and cat food left outside after dark are favorites. Roof rats eat Queen Palm tree fruits in the summer when citrus isn’t available.
Water sources include leaky faucets and sprinkler heads, bird baths, fountains and ornamental ponds, irrigation, air conditioner condensation drip lines, saucers under potted plants, and pet water dishes. They will chew through metal and plastic pipes to reach water.
How do I seal my home?
The most extensive damage occurs when roof rats enter the home, so the first goal is to keep them out.
Use stucco diamond mesh available at building material suppliers to screen and seal all holes and vents leading into your home or garden shed. It cuts and molds very easily. For the rat, this mesh is like biting into small razor blades.
Look for holes in exterior walls and near hot water heaters, washers and dryers, dishwashers, and under sinks. Don’t forget to screen off the sewer stacks on the roof.
All cracks should be caulked.
Stuff the cover of the air conditioning line that runs from the outside unit into the attic with steel wool or copper mesh to prevent rats from climbing up the insulated pipe inside the cover. Look for scratch marks on the insulation, and then set a snap trap there to catch them the next time they use that entrance.
Harvesting citrus and other fruit
Pick all fruit (ripe or not) on citrus and other fruit and nut trees and pick up any fallen fruit. Do this promptly and completely. Fruit and nut trees having the most activity are the ones which come in contact with other trees, houses, fences or with power lines running through.
Donate any excess fruit your family won’t be able to eat to the closest food bank..
Next winter, when the roof rats are under control or eradicated altogether, enjoy your harvest, but be sure to pick your fruit promptly and donate what you can’t use. You don’t need to remove fruit trees from your landscape.
A clean yard is a deterrent.
Rake under your trees and shrubbery. Prune fruit trees so the ground under them is open and visible. Remove wood piles and brush piles from your yard. Store wood and lumber piles at least 18 inches above the ground and 12 inches away from walls. Thick ground covers should be thinned.
Keep your palm trees trimmed. Roof rats nest in the skirts of old fronds, as well as in piles of debris and hollow trees.
Thin out bushes until you can see daylight through them. Oleanders are particularly prone to harbor roof rats in the summer. Thin bougainvilleas as well.
Don’t feed them!
Don’t leave pet food out, especially overnight. Keep dog feces picked up.
It would be best to stop filling your bird feeders for the next few months. Otherwise, provide just the amount of bird seed that will be consumed in a day and sweep up fallen seeds on the ground before sunset. Store bags of bird seed in sealed, rat-proof containers.
Store bulk foods in sealed, rat-proof containers.
Keep garbage containers tightly covered.
What doesn’t work
Rats quickly learn safe travel routes through yards to avoid dogs. Cats will kill dispersing juvenile rats, but are rarely able to handle an adult roof rat.
There is no evidence that ultrasonic and electromagnetic devices drive rodents away. There is evidence that ultrasonic devices can cause hearing loss in pets, especially dogs.
Maricopa County Vector Control tested Coca Cola (rumor has it that roof rats can’t burp and die from drinking it), but found that it was ineffective. In fact, the rats loved it.
Don’t use d-Con. If pets or wild birds nibble on a rat killed with d-Con, they can become sick.
Long term solutions
Strongly consider xeriscaping your yard. Xeriscape doesn’t have to be gravel and a couple of cactuses. There are many lovely options.
Combine xeriscape with a citrus-free yard to create a very effective control against roof rats.
Maintain a defensive line on your property by continuing the use of bait stations, keeping a clean yard and removing pet food and water dishes at night.
What are common signs of roof rat activity?