How to get rid of a rat nest

What a rat nest actually looks like

Not a neat bird-style construction. A rat nest is a loose mass of shredded material packed into a void: insulation, cardboard, paper, fabric, plastic sheeting, dried grass, chewed-up anything. It is roughly the size of a football, it smells strongly of ammonia, and there will be a heavy concentration of droppings around it — rat droppings are dark and up to about three-quarters of an inch long, far bigger than a mouse's rice-grain.

Around the nest you will usually find:

• Greasy rub marks along the route in and out, from oil in the fur
• Gnaw marks on timber, pipe lagging, cable insulation and plastic
• A worn runway — on soil or dust, a visible track two to three inches wide
• Food caches — a pile of pet biscuits, seed or fruit stones somewhere improbable
• Urine staining that fluoresces under UV light, if you want to be thorough

If what you have found is rice-grain droppings and a grapefruit-sized ball of shredded paper, you are looking at mice rather than rats. Mice vs rats will settle it in a minute, and the two problems need different sized traps — see mouse traps vs rat traps.

Where to look, by species

Which rat you have decides where you look, and the two behave completely differently.

Roof rats (black rats) are climbers. They nest HIGH: attic and roof voids, soffits, the cavity above a suspended ceiling, inside dense ivy on a wall, in palm crowns, in a fruit tree canopy, along a fence line, and on top of kitchen cabinets in a voided ceiling. If you hear noise above you at night, start here. Rats in the attic is the dedicated page.

Norway rats (brown rats) are burrowers. They nest LOW: burrows in soil against a foundation or under a shed, under decking, in a crawl space, behind a compost heap, inside a stacked woodpile, in a drain or sewer void, under a concrete slab. The burrow entrance is a smooth hole two to four inches across with a fan of excavated soil. Rats in the yard covers the outdoor side, and roof rats vs Norway rats tells you which you have.

Both will use a wall cavity, which is the hardest case — see rats in the walls.

Work from the noise, the droppings and the rub marks back toward the void. Rats follow the same routes every night, which is exactly what makes them trappable.

Why you trap before you clear

This is the part most people get backwards, and it costs them weeks.

Rats are neophobic. They avoid new objects in a familiar environment, sometimes for days. If you tear out the nest first, you have changed their environment comprehensively — and now you want to introduce a brand new trap into it. You have made the animals cautious at exactly the moment you need them careless.

They relocate, they do not leave. A colony turned out of a crawl space moves into the wall cavity, the garage, or under the decking. Now you have the same rats somewhere less accessible, and no idea where.

The nest is your best information. It tells you the species, the route, the size of the problem and where the traps should go. Destroy it and you are trapping blind.

And there may be young in it. Clearing a nest with a litter in it is an unpleasant surprise and a welfare problem. Trapping the adults first avoids it.

So: find it, leave it, trap the route.

Setting traps on a rat nest route

Place along the runway, flat against the wall, with the trigger end toward the vertical surface. Rats travel on edges even more rigidly than mice. Put traps between the nest and the food source, not at the nest mouth.

Use enough. Rats breed fast and you are almost never dealing with one. Six traps on the main run is a reasonable start; twelve is not excessive for an established colony.

Pre-bait for several days. Set the traps out unset and baited until the bait is being taken confidently, then set them all on the same night. This is the single most effective technique against neophobia, and skipping it is why so many people report that rats "avoid" their traps. Trap-shy rats covers it in detail.

Secure the trap. A rat can drag a loose trap into a void. Wire or screw it down.

Bait small and sticky. Peanut butter, bacon fat, dried fruit or a nut pressed into the trigger — see best rat trap bait.

Box traps where pets, children or wildlife are about. A rat snap trap has enough force to break a dog's toe. A locked top-loading station used as a trap box gives you all of the placement advantage with none of the risk — and none of the poison.

On poison: we would not, and the reason is on rat trap vs poison. A poisoned rat dies inside the structure, which gives you a smell you cannot reach and a secondary-poisoning risk to any cat, dog, owl or fox that scavenges the body.

Clearing the nest safely

Only once catches have stopped for several days.

Ventilate first. Open the space up and leave it for half an hour before you go in, especially an attic or crawl space.

Gloves and a mask. Rodent urine, droppings and nesting material can carry pathogens, and the hazard increases when dry material is disturbed and becomes airborne. The CDC's rodent cleanup guidance is built around not raising dust.

Spray, wait, bag wet. Soak the nest and the surrounding droppings with a disinfectant or bleach solution, leave it five minutes, then lift everything into a bag while it is still wet. Double bag it and put it straight in the outside bin.

Never sweep or vacuum dry material. This is the one rule on the page that is a health rule rather than a technique rule.

Replace what cannot be cleaned. Contaminated loft insulation, chewed cable, soiled stored goods. Have an electrician check any gnawed wiring — rodent damage to cables is a genuine fire risk, not a theoretical one.

Then wash the surfaces and wash yourself.

Collapse a burrow rather than just filling it. For an outdoor Norway rat burrow, dig the run out and backfill with soil and rubble, or pack it with gravel. A loosely filled hole is simply reopened.

Sealing so it does not come back

Rats need a bigger hole than mice — about half an inch — but they will gnaw a small gap into a large one.

• Quarter-inch hardware cloth over vents, weep holes and openings. Not plastic mesh, not foam alone.
• Cement or metal on anything they have already gnawed at. Rats chew through expanding foam, timber and soft plastic without difficulty.
• Pipe and cable penetrations packed with stainless steel wool and sealed over.
• Roof line, soffits, loose tiles and the gap where a service enters — for roof rats this is the whole game.
• Cut back the climbing routes: ivy on the wall, branches overhanging the roof, a fence line running to the eaves.
• Remove the food: bird feeders, fallen fruit, pet food left out, an open compost heap, an unsecured bin. How to get rid of rats is the complete sequence.

Leave two traps set as permanent monitors in the space where the nest was. A catch six weeks later tells you the entry point is still open.

The short version

Find the nest and leave it alone. Pre-bait, then trap the runway between the nest and the food, using enough traps and securing each one. When catches stop, clear the nest wet — spray, wait, bag, never sweep. Then seal with hardware cloth and metal, remove the food, and keep two traps running. Clearing first is the mistake that turns a two-week job into a two-month one.