Mouse Mus musculus

About this pest

KEY CLUES

Distinctive features: Small furry rodent, with long thin tail that is about the same length as the body. Long whiskers. Grey-brown above, with white, grey or brown belly. Female has 10-12 nipples on the belly.

Size: Maximum body length, without tail, around 115mm, and weight around 15-20g, reaching a maximum of 30g.

Droppings: Very small pellets, 3.9-7.6mm long, deposited singly wherever they go.

Footprints: Four toes on forefoot, five on hindfoot. Prints are very small and can look like scattered dots.

Kill signs: Tiny (0.5mm wide) double incisor marks.

Vegetation damage: Eats seeds and small fruits.

Eye shine: TBC

Distribution: Throughout New Zealand – bush, pasture, towns, farms, and at high altitude above the tree-line

WHY ARE HOUSE MICE PESTS?

Ecological impacts

Like all rodent species present in New Zealand, house mice are omnivorous and get their dietary requirements from a wide range of sources. They feed on plant and animal material, and have very flexible feeding behaviour to take advantage of whatever food sources become available. Plant food is usually seeds, but green parts are also eaten. Invertebrates (including insects and spiders) are usually the main species eaten, but bird eggs and chicks and lizards may also be consumed.

The broad diet of mice means that their impacts are equally broad and can be observed through the entire ecosystem. They can affect nutrient cycling within ecosystems by eating the insect larvae that break down leaf litter, therefore preventing the nutrients in the leaf litter returning to the soil. Selective predation of certain seeds can prevent regeneration and alter forest plant species composition. Mice have been recorded feeding on inanga eggs in estuaries, which could have an impact on whitebait runs. On Gough Island in the sub-Antarctic, mice have learned that petrel and albatross chicks are a good food source and they start eating chicks that are still alive.

Mice are a key food source for stoats and feral cats in the New Zealand bush. When conditions are right and there is plenty of food, mouse numbers can increase rapidly. This can occur both in beech forest systems and in tussock grasslandsand results in population growth of mouse predators. These predators feed on native species as well as mice, and during high predator years predation on native birds increases dramatically and can cause local population collapse.

Other impacts

Mice frequently invade houses and damage many things they come into contact with, either by urinating or defecating on it, eating it, chewing it, or a combination of all of these activities.

Read more about mice


Droppings

Separate

Mouse droppings are 3.9 mm to 7.6 mm long and are dark brown or black. They have a distinctive strong ‘soiled’ smell. They scatter single droppings as they run, but there may be groups of droppings where they stop to feed or where they use the same path several times.

Can be confused with:
Large mouse droppings could be mistaken as juvenile kiore or ship rat droppings. Mouse droppings may be confused with weta droppings, but weta droppings have a blunter end and often have a ridge running along the length of the dropping on one side. Stick-insect droppings can look like a tube of stacked circular disks, especially when dry.

Not the droppings you were looking for?

Have a look at all our droppings clues.

Footprints and Tracks

Paws and feet

House mouse prints are very small and on a tracking paper they can look like a scattering of dots. Mice seem to run backwards and forwards and leave prints everywhere and it can be difficult to distinguish individual prints. They can sometimes obscure prints from other species so it is important to check the cards very carefully for other prints that might be hidden under the mouse prints. It is important to look at how the dots are arranged, as weta, stick insects, other insects, and lizards also leave dotty-footprints, but in quite different patterns.

House mouse forefeet prints can be about 7.4mm wide and 5.1mm long, with four toes widely spaced in a circular pattern around up to three central pads. The hind feet prints are about 7.4mm wide and 6.74mm long and have five toes, with the middle three toes in front of the main pad (can be split into up to five segments) and the outer toes are either side of the main pad.

 

Can be confused with:
Mouse prints are unlikely to be mistaken for any other mammal, but other species can create ‘false’ mouse prints. Some silvereyes and blackbirds seem to develop a taste for peanut butter and enter tracking tunnels. The footprints they leave can be quite indistinct and can resemble mouse prints. They have been responsible for several moments of panic in supposedly mouse-free areas, but closer examination usually shows tiny lines across the print left by the scales on the bird’s feet. Blackbirds also seem to be quite aggressive towards the tracking ink and quite often peck marks are visible where they have attacked it. Insects can also leave small footprints, but the grouping of dots (often in straight lines) is quite different to a mouse print. Lizard prints are also quite different: > see some examples.

Dens and nests

House mice dig small burrows for nests or make nests underneath logs or in wall linings in buildings. The very small entrance holes and the small tooth marks left on timber in buildings will identify the species as a mouse.

Can be confused with:
Other rodents, but the entrance holes, footprints, and tooth marks made by other species will be wider.

Not the footprints or tracks you were looking for?

Have a look at all of our tracks.

Vegetation Damage

Fruits and Flowers

Mouse damaged fruit and seeds can be identified by the presence of tiny (approximately 0.5mm wide) parallel incisor marks.

Can be confused with:
Rats leave similar parallel marks, but they are 2-6mm wide depending on the species.

Not the vegetation damage you were looking for?

Browse all types of vegetation damage.

Kill Sign

Fur, feathers or scales (vertebrate)

Birds

Mice may eat small eggs and nestlings but they are not usually considered a major cause of nest predation. However, rock wren populations in alpine environments could be at risk during mouse outbreaks.

Could be confused with:

Nest kill by other predators, including scavenged remains.

Insects or snails (invertebrate)

Mice will chew holes into snail shells to access the animal within. Mouse damaged snail shells can be identified by the presence of tiny (approximately 0.5 mm wide) parallel incisor marks. They are voracious predators of insects, spiders, worms, and beetles but they tend to eat the entire animal so no remains are left.

Can be confused with:
Rats leave similar parallel marks, but they are 2-5mm wide depending on the species.

Not the kill signs you were looking for?

Have a look at all our kill signs.

Other Clues

Smell

Mouse infestations leave an unpleasant musty soiled smell that is caused by acetate in their droppings and urine.

Can be confused with:
May be confused with rat infestations, but the size of the droppings will be much larger for rats.

Sound

High-frequency squeaking.

Can be confused with:
Other rodents, but mice squeaks tend to be higher pitched.

Body covering

Soft brown fur.

Can be confused with:

Other rodent species, although mouse fur will be the shortest of them all.

Bite marks

Mice (like rats) have four incisor teeth at the front of the jaw (two top and two bottom). These long front teeth grow continuously so the animal must gnaw or chew enough to keep wearing them down. Mice have no canine teeth, a premolar midway back on each side of the bottom jaw and three molars, top and bottom, at the back on each side. 

For guidance on identifying mouse bite marks go to Landcare Research, 'Rodents' heading or pages 17-19 of their identification guide.

Distribution

Found on North Island and South Island and on many offshore islands. They live from the coast to high altitudes, and have been found at more than 1,300 m above sea level. Areas with high Norway rat numbers tend to have low mouse numbers. Mice are very difficult to eradicate and can re-invade quickly on the mainland. The have been successfully eradicated from several offshore islands.

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MORE ABOUT MICE

Origin

House mice probably originated in India and spread across Europe aided by people. They found their way onto sailing ships and got transported around the world. The first mouse arrived in New Zealand via Australia when the Henrietta ran ashore on Ruapuke Island off Stewart Island in 1824.

Description

The mouse is a small rodent with a long thin tail that is about the same length as the head and body combined. Mice in New Zealand are generally grey-brown above with a grey, white or brown belly.

Size and weight

Maximum head-body length is 115mm, excluding the tail. Adult weight ranges from 15 g to 20 g with a maximum of about 30g.

Behaviour

Mice are mostly nocturnal and are most active around dusk and dawn. They have reduced activity in daylight hours, but will occasionally forage during this period. They dig small burrows for nests or make nests underneath logs or in wall linings in buildings.

Diet

Mice eat a very wide range of plant and animal material.

Habitat

Mice can live in all New Zealand habitats. They are commonly found in overgrown areas where they have protection from rats, are common home invaders, and can be a real problem in cities and around farms.

Distribution in New Zealand

See distribution clue.

Other

“Mouse plagues” occur periodically in grain growing areas of Australia. At the peak of a plague, mice can reach densities of 1000 per hectare and vast areas are completely overwhelmed by them.

How to get rid of mice

Contact your local DOC or Regional Council office for advice (see Next Steps). Poisoning and trapping.


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FIND MORE INFORMATION IN

Baker, C. F. (2006). Predation of inanga (Galaxias maculatus) eggs by field mice (Mus musculus). Journal of the Royal Society of New Zealand, 36, 143-147.

Michelsen-Heath S., and Gaze P. (2007). Changes in abundance and distribution of the rock wren (Xenicus gilviventris) in the South Island, New Zealand. Notornis 54, 71-78.

O'Donnell, C. F. (1996). Predators and the decline of New Zealand forest birds: an introduction to the hole‐nesting bird and predator programme. New Zealand Journal of Zoology, 23, 213-219.

Ratz H. (1997). Identification of footprints of some small mammals. Mammalia, 61(3), 431-441.

Ruscoe W.A., & Murphy E.C. (2005). House mouse. In King, C.M., (Ed.), The handbook of New Zealand mammals (pp. 204-222). Auckland: Oxford University Press.

Wanless, R. M., Angel, A., Cuthbert, R. J., Hilton, G. M., & Ryan, P. G. (2007). Can predation by invasive mice drive seabird extinctions? Biology letters, 3, 241-244.

Wilson D.J., & Lee W.G. (2010). Primary and secondary resource pulses in an alpine ecosystem: snow tussock grass (Chionochloa spp.) flowering and house mouse (Mus musculus) populations in New Zealand. Wildlife Research, 37, 89–103.