Brown ratRattus norvegicus — identification, signs & control

• Head and body 20–27 cm, tail 17–23 cm, and adults usually weigh 200–500 g: several times heavier than any mouse.
• Blunt, rounded snout and small, finely haired ears that do not reach the eyes when folded forward.
• Coarse grey-brown fur on the back, fading to pale grey or off-white underneath.
• Thick, scaly tail, darker on top than underneath and shorter than the head and body combined.
• Young rats have oversized heads and feet for their bodies and are often mistaken for large mice.
• Runs along walls, fence bases and pipes on the same routes every night, mostly between dusk and dawn.

Droppings

Dark, capsule-shaped, 10–14 mm long, usually in small clusters along runs or near food.

Runs and smear marks

Flattened tracks through grass, and dark greasy rub marks on skirting, joists and pipes where fur brushes the surface.

Burrows

Holes 6–9 cm across with smooth, packed entrances under decking, sheds, compost bins or at the base of walls.

Gnawing

Paired tooth marks on wood, plastic pipe and cable sheathing. Fresh gnawing is pale; old gnawing darkens.

Noises

Scratching and heavier scurrying at night in ceilings, under floors or behind kitchen units.

Smell and footprints

A sharp ammonia smell in enclosed spaces; footprints and tail-drag lines in dust or mud.

Brown rats live in family groups and dig burrows in soft ground, under decking and sheds, and along banks. In towns many live in the sewers and reach houses through broken or disused drain pipes, which is why a rat can turn up in a kitchen with no hole in any outside wall. They are wary of anything new, so a trap or bait box can be ignored for several days. A female can breed from about three months old, has litters of six to eleven after a three-week pregnancy and can raise five litters a year. They eat almost anything: bird seed, compost, pet food and bin waste.

Rat urine can carry the bacteria that cause leptospirosis, including its severe form, Weil's disease. It is uncommon in the UK, but people who work around water, sewers or farms, or who clear up after rats without gloves, carry the most risk. Rats also spread salmonella and other gut bacteria onto worktops and food. Their teeth never stop growing, so they gnaw constantly: through electrical cable insulation (a fire risk), plastic waste pipes, lead flashing and loft insulation. Burrows under patios and paths can make slabs sink.

The Prevention of Damage by Pests Act 1949 requires the occupier of land to tell the local council in writing if rats or mice are living on or visiting it in substantial numbers (agricultural land is excluded), and lets the council order the owner to deal with them. Stronger rodenticides can only be bought and used by trained, certified users under the UK rodenticide stewardship regime, following the CRRU Code. In England, using a glue trap on a rodent is an offence without a licence.

One rat seen once in the garden, near a bird feeder, is often something you can handle yourself: take the feeder down, clear spilt food, and set snap traps inside a covered box or tunnel so pets and birds cannot reach them. Rats indoors are a different job. If you hear them in the ceiling or find droppings in a kitchen cupboard, the real work is finding how they get in, and that is often a broken drain rather than a hole you can see. Shop-bought poison laid in the open puts pets, children and wildlife at risk, and a rat that dies under the floor smells for weeks.

We start with a free inspection: droppings, runs and gnaw marks tell us roughly how many rats there are, where they are living and how they are getting in. Treatment is usually tamper-resistant bait boxes or traps placed on their runs in line with the CRRU Code, followed by return visits to check activity, remove dead rats and collect unused bait. Where rats are coming up from a drain we check inspection chambers and pipe runs for damage, and we proof gaps, air bricks and pipe entries with rodent-resistant materials. You get a written record of what was used and where. Rat treatment starts from £90.

1. 1Hang bird feeders over a tray or hard surface and sweep up spilt seed every evening; a pile of seed under a feeder feeds rats every night.
2. 2Use a closed compost bin on a paving slab or wire-mesh base, and keep cooked food, meat and bread out of it.
3. 3Keep drain covers and inspection chamber lids in place, and have cracked or disused pipes repaired or capped.
4. 4Seal gaps of 15 mm or more around pipes, cables and air bricks with steel mesh, metal plates or mortar; rats chew through foam and plastic filler.
5. 5Store pet food, chicken feed and bird seed in metal bins or thick plastic containers with tight lids.
6. 6Clear clutter and log piles from against the house walls, and lift a decking board now and then to check for burrows.

Brown rats follow water, and Hertfordshire has plenty of it: the chalk rivers Ver, Colne, Gade and Lea, and the Grand Union Canal through Rickmansworth, Kings Langley and Berkhamsted. Many Victorian terraces in St Albans still drain through old clay pipes, where a cracked joint gives sewer rats a route in. Homes backing onto farmland also see more activity after harvest, when rats move from the fields into gardens and outbuildings.

Local pages: Rat control in St Albans · all areas