How to Get Rid of Rats (snap traps and exclusion, how rats differ from mice)

The short answer

Set rat-sized snap traps (not mouse traps) along walls where droppings or rub marks show travel, bait them with a sticky smear like peanut butter, and space them ten to twenty feet apart. University of Missouri Extension is direct: in a heavily infested home, “a dozen or more traps may be needed.” Then seal anything bigger than a quarter inch, since both rats and mice fit through a quarter inch gap and an adult rat only needs about half an inch. Most DIY failures are the same three things: using a mouse trap on a rat, setting too few traps, or sealing only what is easy to reach.

Rats are not just big mice

If you have caught mice before, the reflex is to set the same trap and call it a day. It will not work on a rat, and the rules are different.

• Body. Utah State University Extension puts the average Norway rat at about 16 inches head to tail, and University of Illinois Extension puts the body mass at typically 0.5 to 1 lb. A mouse-rated snap trap has a mouse-sized trigger and kill bar; it often fails on a rat humanely or at all.
• Droppings. Rat droppings are 1/2 to 3/4 inch long, blunt-ended on Norway rats and more pointed on roof rats, per NC State. Mouse droppings are much smaller. NC State also puts rat output at 30 to 50 droppings per rat per day, so a fresh pile under the sink is a rat from last night, not last month.
• Travel. Missouri puts the home range at about 100 to 150 feet in diameter, and says rats “seldom travel farther than 300 feet from their burrows for food or water.” A rat in the garage is living under the slab or in the next-door burrow.
• Reproduction. Missouri puts litters at 6 to 12 young with 4 to 6 litters a year, breeding most actively in spring and fall. A problem that has been sitting for a season or two is past what a weekend of effort will resolve.

Two species cause almost every US rat problem, and they are not interchangeable.

• Norway rat (Rattus norvegicus). Stocky, brown, small eyes and ears, blunt snout, tail shorter than the body. ICWDM, Illinois Extension, and Missouri all describe them as burrowers. Indoors they live at or below ground level: basements, crawlspaces, foundation voids, slab edges.
• Roof rat (Rattus rattus). Slimmer, longer tail (NC State: often longer than the body), larger ears and eyes. NC State puts roof rats in elevated areas and Norway rats underground; ICWDM is more specific, describing roof rats living in trees such as palm, on vine-covered fences, and in attics they reach from the roof or along overhead utility lines. Droppings are pointier than Norway rat droppings. Scratching above the ceiling usually means roof rats; burrows next to the foundation usually mean Norway rats. Sealing a foundation burrow without trimming the vines off the wall gets you a roof rat in the attic.

Traps that actually catch rats

Use rat-sized snap traps. Missouri and NC State both recommend rat-sized snap traps, for the same reasons: they kill quickly, they give you a count of what you have caught, and they do not leave a poisoned carcass to die in the wall.

• Bait. Sticky baits the rat has to gnaw off the trigger: peanut butter or honey per NC State, or a piece of hot dog, bacon, or nutmeat “tied securely to the trigger” per Missouri and ICWDM. Press the bait into the trigger pedal so the rat has to tug, not grab.
• Placement. Set the trap flush to the wall with the trigger against the baseboard, then space them 10 to 20 feet apart, not the 3-foot spacing that works for mice. Pairs back-to-back catch rats from either direction. Corners, behind the stove, along the basement perimeter, and the dark edge of the garage are good starting points. Missouri: a rat traveling along a wall should pass directly over the trigger.
• Count. A dozen traps is a normal starting number for an established infestation, per Missouri. Under-trapping is the most common reason a rat program stalls.
• Pre-bait. Bait and unset the traps for several nights before arming them. Rats are wary of new objects.

Glue boards are less effective for rats than for mice, per Missouri, and both Missouri and NC State warn they catch non-target wildlife such as lizards and birds. Skip them.

Most consumer rodenticides are anticoagulant baits. They can work, but the rat dies somewhere you cannot reach, and for days your house smells like it. Missouri notes the strongest anticoagulants, such as brodifacoum and bromadiolone, can be lethal in a single feeding, and that a rat that eats a lethal dose usually dies two to six days later. Snap traps let you see what you caught.

Sealing that actually keeps rats out

Missouri and ICWDM both lead their exclusion guidance with a gap threshold. Missouri says any opening larger than 1/4 inch should be closed to exclude both rats and mice, and ICWDM says to seal every opening larger than 1/2 inch to exclude rats. Either way, a gap that looks “too small for a rat” often is not.

Walk the outside in daylight with a flashlight and look, in this order:

• Foundation and sill plate. Settled foundations open seams where the wood framing meets the concrete. Norway rats burrow along foundation walls and use these gaps.
• Pipe, wire, and conduit penetrations. Every hose bib, gas line, dryer vent, AC line set, and cable box has trim around it; the gap beside the trim is the entry.
• Garage door corners and the gap under the door. A worn corner seal leaves a triangular gap a rat walks through.
• Weep holes. Do not seal them solid; they need to drain. Stuff them with copper mesh.
• Vents. Cover attic, crawlspace, and foundation vents with 19- or 24-gauge hardware cloth, per Missouri.
• Roofline. Soffit-to-fascia seams, plumbing vent stacks, where wires enter the attic. Roof rats use the eaves as a highway.

For the gap a rat is using, pack steel wool or copper mesh tightly, then seal over it with caulk or cement. Both EPA and Missouri name steel wool as the standard plug. Missouri calls packed steel wool a good temporary fix and notes a lasting repair wants a durable material over the top. Sheet metal or cement patches handle gnawed corners. NC State is blunt that rats chew through expanding foam, so it should not be the barrier; NC State says to caulk over packed steel wool or copper mesh, since rats can otherwise push the mesh aside.

Repellents do not work. NC State: “repellents are not a reliable form of rat management or prevention.” Peppermint oil, mothballs, ammonia, and ultrasonic plug-ins all fall in this bucket. Missouri notes ultrasound “has not been shown to drive established rodents out of buildings” and cannot be recommended, and that house cats and dogs do not effectively control rat populations.

Clean up safely

Rats and their droppings carry pathogens. NC State: ventilate any enclosed space for 30 minutes before entry, wear gloves plus a respirator or mask and goggles, and coat droppings with a 10 percent bleach solution before wiping them up. Do not sweep dry droppings; that puts particles in the air. Pick up dead rats with a sturdy plastic bag inverted over your hand, seal it, and put it out with the household trash, per Missouri.

The mistake almost everyone makes

Treating this as a mouse problem. Mouse traps are too small. Mouse-trap spacing leaves 10-foot gaps along a rat run. A quarter-inch threshold is a real entry for a mouse and a near-miss for a rat, so a “sealed” house with quarter-inch-plus gaps is a sealed mouse house and an open rat hotel. The other common mistake is sealing the inside first, before trapping and sealing outside in. The interior hole where a rat enters the wall is rarely the same as the exterior one.

When to call a pro

A licensed pest professional is the right call when:

• You are still catching new rats after two to three weeks of well-set traps plus sealing. The entry point is somewhere you cannot reach.
• You hear activity in ceilings or wall voids you cannot access.
• Droppings are showing up in multiple rooms, which usually means multiple entry points a flashlight cannot find.
• You have an outbuilding, barn, or chicken coop with a long-standing problem, where sanitation and rodent-proof construction usually matter more than trapping alone.
• You would rather not handle rodenticide placement yourself. A licensed applicator can place tamper-resistant bait stations where children, pets, and non-target wildlife cannot reach them.

Traps clear the rats you have. Exclusion ends the problem. The houses that stay rat-free are the ones where the sealing got done while the traps were still catching.