Guides · Watford

Rat or Mouse? How to Tell What You Have

Knowing whether you have rats or mice changes the treatment, the cost and how urgently it needs dealing with, and it is usually possible to tell from the evidence they leave behind. This page sets out the differences so you can describe the problem accurately when you call someone.

Droppings are the clearest sign

Mouse droppings are roughly the size of a grain of rice, about 3 to 6mm long, dark, and pointed at both ends. You will typically find a lot of them, scattered widely, because a mouse produces dozens a day as it moves. Rat droppings are far larger - 10 to 20mm, about the size and shape of an olive pip or a large grain of brown rice, and blunter at the ends. Rats also tend to leave them concentrated in fewer places along regular routes rather than scattered throughout. Fresh droppings are dark and slightly soft; older ones go grey, dry and crumble when disturbed.

What you can hear, and when

Mice produce light, quick scratching and scurrying, usually high up - in the loft, in wall cavities, above ceilings - and often sound almost continuous because they move constantly. Rats are heavier and slower, and the sound is more of a thump or a drag than a scurry. Rats are also more often heard below floor level, under suspended timber floors or in cellars, because they enter from drains and burrows rather than from the roofline. Both are most active at night, and hearing activity in daylight generally means a larger, more established population.

Damage and entry points

Mice can get through a gap the width of a pencil, around 6mm, which is why proofing a mouse infestation is painstaking work. Rats need a larger gap, around 20mm, but will gnaw to enlarge one, and can damage lead pipe, plastic waste pipe and even soft mortar. Rats also enter via defective drains, which mice do not, so a persistent rat problem with no obvious external entry point is a reason to have the drainage checked. Chewed electrical cable is common to both and is the most serious risk either poses.

What this means locally

Around Watford the pattern follows the geography. Properties backing onto the Grand Union Canal, the River Colne and the Croxley and Rickmansworth waterways see genuine rat pressure, particularly in autumn as temperatures drop and populations move inland from the banks into gardens and then into buildings. Rat activity here often traces back to burrows in soft ground near water, or to drain defects. Mice are far more common in the older terraced and inter-war housing across Watford, Callowland and Oxhey, where suspended floors, original airbricks and shared voids in converted properties give them routes through a building that are almost impossible to see from inside.

Common questions

Can I have both at once?

It is possible but uncommon in the same space. Rats are territorial and will generally displace mice, so a property with an established rat population usually will not also have mice in the same area. Finding both types of dropping often means the mouse activity is older than the rat activity.

Is one more urgent than the other?

Rats, generally. They cause more structural and wiring damage, carry a wider disease risk, breed prolifically, and their link to drains means a rat problem is sometimes also a drainage problem. That said, mice reproduce very fast and a small mouse problem becomes a large one within a few weeks, so neither is worth leaving.

Should I try shop-bought bait first?

It rarely resolves an established infestation and can make treatment harder. Bait placed in the wrong location teaches rodents to avoid it, and poisoned rodents dying inside a cavity or under a floor create a serious smell problem that is far more difficult to deal with than the original infestation. Traps are a reasonable stopgap for one or two mice; anything beyond that is worth having surveyed.