Rat infestations are more than annoyances; they're potential health and safety hazards. The most effective strategies for your situation will depend on the source of your infestation, the type of rat you're dealing with and the location of your home.
Start by taking a picture of a rat in your home if you can, as identifying its species will help you determine its food source and general habits. The most common species in the United States are roof rats and Norway (sewer) rats. Once you know what you're dealing with, consider these strategies for keeping your home and yard rat-free.
Check the cracks
Prevention or "exclusion" is a major step toward stopping or shortening your next rat infestation. To that end, you'll want to check your home for weak spots or holes where rats could get in. Certain types of rats are accomplished climbers, which means they could be entering through attic vents or the roof. You'll also want to check your foundation, crawl space and anywhere wires or pipes enter your home for gaps or cracks.
The University of Arizona Cooperative Extension suggests you seal any openings that are 1/2-inch or wider, connecting them to the outside of a structure with concrete mortar, steel or copper wool, or metal flashing.
Change the environment
If prevention hasn't worked, consider how to change your home and yard to make them less inviting refuges for the rats. Jim Osborn, an expert on all things pest in the northwest, notes that bird feeders and bird seed are one of the biggest attractants for roof rats. Throw all garbage away in rodent-proof containers. If you have food storage rooms or food stored in the garage, make those places similarly difficult for your little unwanted guests to access.
Do you grow fruits or vegetables in a greenhouse or in your yard? Harvest the produce when it's ripe, and quickly clean up any fallen or rotten fruit. Keep your yard tidy and free from tall weeds or other cover the rodents could use to hide under. Keep trees pruned so they don't overhang your roof and the branches don't touch fences or overhead wires that could provide climbing rats access to your roof.
If you suspect the rat colony you're combatting is fairly small or you see rats only intermittently, trapping can be an effective means of ridding your home of its rat problem. Place the traps in places you've seen rats. Look for "rat runways," where you can tell they travel frequently.
If you don't get results right away, keep up your persistence. Rats are naturally cautious and may avoid traps for a few days. You can also try pre-baiting the traps by baiting them but not setting them. Once the rats become accustomed to the traps, re-bait and set them. According to Paratex, both Norway and roof rats are attracted to baits like meat, fish, cereal, fruit, vegetables and pet food. They also need a lot of fresh water, so consider placing traps near possible water sources.
Baits can be effective against rat infestations, but they are also dangerous to children and domestic animals. They are best used with childproof bait stations and should be placed in locations only rats are likely to come across them. Be aware that rats do not die immediately upon consuming the bait, so make sure they can't get into any inaccessible places in your home, or else you'll end up with a new problem: dead rat odor.
If these methods don't work for you, it may be time to call in a professional