Rattus norvegicus | Brown Rat | Francach



Conservation status

Least Concern

Legal status

Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted). Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).

First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Transport Stowaway

Introduction pathways subclass - 1

Hitchhikers on ship/boat

Invasive score


NAPRA Ireland risk assessed


Species Biology


Larger, longer tailed and with a pointed muzzle and broader longer hind feet, compared to smaller rodent species (Quy & MacDonald, 2008). Distinguished from Rattus rattus by relatively smaller eyes and ears, with hair on the ears (Quy & MacDonald, 2008). Colour not diagnostic, black rats may be brown and brown rats may be black, however black rats in Ireland are thought to be restricted to Lambay Island.


Considered an 'obligate pest', in that across most of their geographical range their survival is based on human agricultural production, with the level of damage varying according to the scale of the agricultural system being exploited (Alpin et al., 2003). Generally do not tend to survive well in natural ecosystems (Alpin et al., 2003), their effects on wildlife are largely confined to islands, particularly those with endemics not adapted to mammalian predators such as New Zealand (Jones et al., 2008; Towns et al., 2006). Negative impacts have been recorded for flightless invertebrates, ground-dwelling reptiles, land birds, and burrowing seabirds (Towns et al., 2006), while globally, ship rats have been associated with the decline in 60 indigenous vertebrate species (Towns et al., 2006) and rats in general with the decline of 75 seabird species globally (Jones et al., 2008).


Constructed, industrial or other artificial habitats


Promiscuous mating system producing, on average, produce 5 litters of 9 pups annually (Quy & MacDonald, 2008).

Pathway and vector description

Introduced into Europe and then Ireland from China in the 18th century, displacing the ship or black rat (Rattus rattus) (Quy & MacDonald, 2008). While it is unlikely that an effective control of rats will be developed due to their behavioural plasticity (Quy & MacDonald, 2008), care should be taken to avoid spread to any off shore islands that may currently be rat free.

Mechanism of impact


Broad environment


Habitat description

While highly adaptable and versatile suffer from competition in the wild and typically occur where food is augmented by human activities, though not an obligate commensal (Quy & MacDonald, 2008), they are commensal (found in association with humans) and do not tend to survive well in natural environments (Alpin et al., 2003).

Species group


Native region

Temperate Asia

Similar species

Black rat (Rattus rattus)


World distribution(GBIF)

Irish distribution

Established - Widespread & Common

Native distribution

Originally from the steppes of Central Asia (Quy & McDonald, 2008).

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2020

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How can you help

Report any sightings to the National Biodiversity Data Centre.

Further information

Delivering Alien Invasive Species In Europe (DAISIE) project list this as one of the 100 Worst Invaders in Europe.



Quy, R.J. & MacDonald, D.W. (2008). Genus Rattus Common rat - Rattus norvegicus In: Mammals of the British Isles : Handbook, 4th edition Harris, S. & Yalden, D.W. (eds) The Mammal Society, UK. Aplin, K. P., Chesser, T., & Have, J. T. (2003). Evolutionary biology of the genus Rattus: profile of an archetypal rodent pest. In: Singleton GR, Hinds LA, Krebs CJ, Spratt DM (eds) Rats, mice and people: rodent biology and management. ACIAR, Canberra, pp 487–498. Feng, A. Y., & Himsworth, C. G. (2014). The secret life of the city rat: a review of the ecology of urban Norway and black rats (Rattus norvegicus and Rattus rattus). Urban ecosystems, 17(1), 149-162.Jones, H. P., Tershy, B. R., Zavaleta, E. S., Croll, D. A., Keitt, B. S., Finkelstein, M. E., & Howald, G. R. (2008). Severity of the effects of invasive rats on seabirds: a global review. Conservation Biology, 22(1), 16-26. Towns, D. R., Atkinson, I. A., & Daugherty, C. H. (2006). Have the harmful effects of introduced rats on islands been exaggerated?. Biological invasions, 8(4), 863-891.

Global Invasive Species Database

IUCN Red List of Threatened Species

Atlas of Irish Mammals

CABI Datasheet

DAISIE Factsheet