California is home to two widespread invasive rat species, roof rats and Norway rats, found in nearly every city across the state. A handful of native species, including woodrats (pack rats), also live in and around homes in more rural areas. Whether you’re trying to identify a rat you’ve spotted, understand the health risks, or keep them out of your house, here’s what you need to know.
Which Rat Species Live in California
The two dominant species are roof rats (sometimes called black rats) and Norway rats. Both are invasive, originally arriving on ships, and they now thrive in urban and suburban environments statewide. These are the rats you’ll encounter in attics, garages, yards, and near dumpsters.
Native woodrats, also called pack rats, are a separate group entirely. They’re more common in rural and semi-rural areas and occasionally show up around homes near open land. The quickest way to tell them apart from roof and Norway rats: woodrats have furry tails, while the invasive species have scaly, mostly hairless tails.
Roof Rats vs. Norway Rats
Roof rats are the more agile of the two. They weigh 5 to 10 ounces, have a sleek build, pointed muzzle, and large ears that reach the eyes when folded forward. Their tail is the giveaway: it’s uniformly dark and long enough to extend past the nose when pulled over the back. True to their name, they prefer elevated spaces, nesting in trees, attics, and along rooflines.
Norway rats are the bruisers. They weigh 7 to 18 ounces, have a robust build, blunt muzzle, and smaller ears that don’t reach the eyes. Their tail is shorter relative to their body, reaching only the middle of the skull when pulled back, and it’s dark on top with a paler underside. Norway rats tend to stay lower, burrowing along foundations, under sheds, and in crawlspaces.
Where They Nest and What They Eat
Roof rats are especially common in California’s citrus and avocado-growing regions. They build nests from leaves and twigs in fruit trees, or settle into debris piles, thick mulch, and shallow burrows. In nut orchards, they nest around the base of trees. In barns and feed yards, they burrow under feed bunks or into hay bales.
Their diet reflects California’s agriculture. Roof rats feed heavily on oranges, avocados, and other fruits, sometimes hollowing out the skin and leaving it hanging on the tree. If you’ve found a citrus fruit with a clean, round hole gnawed into it, that’s a classic roof rat sign. Both species also gnaw on electrical wires and wooden structures, which creates fire hazards and costly damage. Rats are active year-round and almost exclusively at night, so you may hear them before you see them.
Health Risks From Rats in California
Flea-borne typhus is the most pressing rat-linked disease concern in California right now. Los Angeles County documented an all-time high of 220 cases in 2025, continuing a sustained upward trend since 2010. Clusters have appeared primarily in Central and South Los Angeles. The disease spreads through fleas carried by rats, free-roaming cats, and opossums. Symptoms include fever, headache, and rash, and while it’s treatable with antibiotics, it can become serious if missed.
Hantavirus is a common worry, but the picture is more nuanced than most people realize. In California and the broader western U.S., the primary carrier is the deer mouse, not common house rats or roof rats. Hantavirus spreads through contact with infected rodent droppings, urine, or saliva, typically when cleaning enclosed spaces where deer mice have nested. Standard urban rats are not known carriers.
Rats can still transmit other illnesses through contaminated food, droppings, and direct bites. Keeping them out of your living space matters for sanitation as much as comfort.
California’s Restrictions on Rat Poison
California has some of the strictest rodenticide laws in the country. In 2020, Governor Newsom signed AB 1788, banning the use of four second-generation anticoagulant rodenticides (the most potent rat poisons) because they were poisoning mountain lions, hawks, and other wildlife up the food chain. The ban took effect January 1, 2021.
Prohibited uses include homes, restaurants, grocery stores, schools, airports, offices, shopping malls, parks, and construction sites. The only exemptions are narrow: certified vector control technicians employed by government agencies, and government employees protecting water supply infrastructure like reservoirs and treatment plants. For most homeowners and businesses, these products are simply off the table.
This means exclusion and trapping are the primary tools available to California residents. First-generation rodenticides and snap traps remain legal, but sealing rats out of your home is the most effective long-term strategy.
How to Keep Rats Out of Your Home
Rat exclusion means finding and sealing every gap a rat could use to enter. Rats can squeeze through openings as small as a quarter. A thorough inspection covers gaps around pipes, vents, utility lines, rooflines, the foundation, attic, and crawlspace. Look for grease marks along walls, droppings, and gnaw damage as signs of active pathways.
The materials matter more than most people think. Foam sealant alone is useless because rats chew through it quickly, creating a false sense of security. Effective barriers use rigid, chew-resistant materials:
- Gaps around pipes and conduits: steel mesh packed in and sealed with exterior-grade caulk
- Vents and weep holes: galvanized mesh covers
- Foundation cracks: concrete patching or metal flashing
- Roof and fascia gaps: metal flashing or hardware cloth
- Garage door gaps: door sweeps or threshold seals
For DIY work, hardware cloth with quarter-inch openings is a reliable choice for covering vents or larger gaps near the foundation. You can cut it to size and secure it with screws or staples. Copper mesh packed into a gap and sealed with exterior caulk works for smaller holes, though it’s not as durable as a professionally installed galvanized steel barrier. Replacing a worn garage door sweep is one of the simplest fixes most homeowners overlook entirely.
Focus your own efforts on reachable, ground-level locations. Roof-level work and confined-space repairs are better left to a professional, both for safety and because roof rats’ elevated entry points are easy to miss without experience. Outside the house, keep fruit trees harvested, thin dense vegetation near walls, store firewood away from the structure, and eliminate standing water sources.