Rodents

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What is the Difference Between a Rat and a Mouse?

There are just three species of rat and mouse that are by far the most prevalent and important pests in homes and businesses worldwide due to their ability to adapt to the human environment.

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

The house mouse has several subspecies that are common in different parts of the world and are increasingly being recognised as separate species, but these are all virtually indistinguishable from each other.

All rodents have the common identifying feature of a pair of incisor teeth in the upper jaw. They tend to have short legs and a long tail, but a closer look at their body characteristics and habits shows that there are easily distinguishable features that you can use to identify which pest is invading your property.

What do mice look like?

The easiest distinguishing feature is the small size of the house mouse at 3-10 cm long.

However, a mouse can be confused with a young rat.

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

What do rats look like?

The brown rat is larger than the ship rat and they have the following differing body features:

Brown rat:

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

Black rat:

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

Rat and mice eating habits

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:

  • Prefers cereals;
  • cuts grain when eating, giving the appearance that is has been chopped;
  • tends to seek food in the same places, making baiting easier;
  • drinks about 60ml water a day;

Black rats:

  • Prefers moist fruit;
  • cuts grain when eating, giving the appearance that is has been chopped;
  • tends 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.
  • drinks about 30ml water a day.

Mice:

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

Where do rats and mice 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 the feet and the surfaces that it travels along show continuous smudges from the oily fur.

Where do black rats live?

Black rats are mainly restricted to buildings around ports and in ships in temperate countries (hence the name ‘ship rat’). They are agile and a good climbers, nesting high up under roofs. In warmer countries, where they originate, black rats will nest in trees, especially in woodland and orchards. Black rats tend to walk on their toes and the surfaces that the ship rat travels along show separated smudges.

Where do mice live?

Mice usually lives on the ground and nests in burrows, but is agile and can climb. In heavy infestations, grease from the body combined with dirt and urine can build into small pillars. These can remain for a long time, so may not indicate a current infestation. A mouse obviously has a smaller footprint than a rat.

Droppings

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 and those from a cockroach.

Brown rat 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

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

Mouse droppings are approximately 3-8mm in length, and are often found scattered randomly during a infestation. Mouse droppings are granular in shape and black in colour and can be found near nesting areas.

Breeding

Mice reach sexual maturity earlier and produce larger litters at a more frequent rate than rats. The new borne of all three rodents are blind, hairless and completely 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