What is the difference between rats and mice?

There are just two species of rats and one species of mice that have become the most common pests in homes and businesses, and this is due to their ability to adapt to the human environment.

These are:  

• The brown rat (Rattus norvegicus, also called the common or Norway rat),
• The black rat (Rattus rattus, also called the roof rat) and
• The house mouse (Mus domesticus).

All rodents can commonly be identified by the pair of incisor teeth in their upper jaw. They have shorter legs and a longer tail, but a closer look at their body characteristics and habits shows that there are recognisable features that you can use to determine which pest is inhabiting your premises.

The most obvious distinguishing feature between rats and mice is size; a house mouse is usually 3-10 cm long.  However, a mouse can be confused with a young rat. Here’s what to look out for:

• A mature mouse can be differentiated from a young rat by its larger ears and longer tail compared to its body length compared to the rat.
• A young rat also has distinctly larger feet and head compared to the body than a mouse.
• Mice are typically light grey or brown in colour with a lighter shade on their bellies.

• thicker body;
• tail shorter than length of head and body;
• paler colour underneath the tail;
• small hairy ears;
• blunt nose.

• slender body;
• large thin ears;
• pointed nose;
• tail longer than head and body.

Both rats and mice are omnivorous, but the brown rat and house mouse prefer cereals, while black rats prefer fruit and foods with a high moisture content.

Brown rats:

• Prefer cereals;
• cut grain when eating, giving the appearance that is has been chopped;
• tend to seek food in the same places, making baiting easier;
• drink about 60ml water a day;

Black rats:

• Prefer moist fruit;
• cut grain when eating, giving the appearance that is has been chopped;
• tend not to eat at the same location on consecutive nights. This makes them more difficult to control, requiring many small baiting points using moist food, which only remains edible for a few days before needing replacing.
• drink about 30ml water a day.

Mice:

•  prefer cereals;
• when eating it ‘kibbles’ the grain by removing the outer husk to eat the white endosperm inside;
• tend to seek food in the same places;
• don’t need to drink water but will drink about 3ml if available.

Where do brown rats live?

Brown rats usually live on the ground and burrows. They are usually spotted throughout buildings, in sewer systems and outdoors. Their burrowing can cause extensive damage to sewers. The brown rat tends to walk on the pads of their feet and the surfaces that it travels along show continuous smudges from the oily fur.

Where do black rats live?

Black rats are mostly confined to buildings around ports and in ships in temperate countries (hence the name ‘ship rat’). They are agile and a good climbers (hence the name ‘roof rat’), nesting high up under roofs, which is why you might hear the scurrying sounds of rats in the ceiling. In warmer countries, where they originate, black rats will nest in trees, especially in woodland and orchards. Black rats walk on their toes and the surfaces that the roof rat travels along show separated smudges.

Where do mice live?

Even though mice usually live on the ground and nest in burrows, they are agile and can climb. In heavy infestations, grease from their body combined with dirt and urine can build into small pillars (referred to as “urine pillars”). These can remain for a long period of time, so may not indicate a current mouse infestation. A mouse obviously has a smaller footprint than a rat.

The droppings of the three animals differ in size and shape, according to the body size. Rat droppings can often been mistaken for mouse droppings or even for cockroach droppings.

• Brown rat droppings are wide and are dark brown colour. They are typically found in a tapered, spindle shape, resembling a large grain of rice.
• Black rat droppings are long and thin, and are smaller than brown rat droppings. Black rat droppings are more regular in form with a banana like curve and pointed ends.
• Mouse droppings are approximately 3-8mm in length, and are often found scattered randomly during an infestation. Mouse droppings are granular in shape and black in colour and can be found near nesting areas.

Mice reach sexual maturity earlier than rats and produce larger litters at a more frequent rate than rats. The newborn of all three rodents are blind, hairless and entirely dependent on the mother for feeding and protection.

House mouse

• litter size: 4-16
• number of litters per year: 7-8
• maturity: 8-12 weeks

Brown rat

• litter size: 7-8
• number of litters per year: 3-6
• time to maturity: 10-12 weeks

Black rat

• litter size: 5-10
• number of litters per year: 3-6
• time to maturity: 7-8 weeks