Asian house rat

    • The Asian house rat, Rattus tanezumi, is an invasive species in South Africa. The species was introduced by human activity into areas beyond their natural range, either inadvertently or by escaping captivity (Witmer et al. 2014). It is recognised as one of the major drivers of global biodiversity change (Keller et al. 2011). Once established, the species successfully invades new areas, and their presence often results in negative ecological, economic and human health impacts (Towns et al., 1994). Rattus tanezumi is associated with several zoonoses and is a common rodent host of ectoparasites. It frequently has a large number of fleas and chiggers (mites) on its skin and vector-borne diseases such as rat-bite fever, plague and leptospirosis can be transmitted from rats to people when fleas and chiggers bite them (Kosoy et al. 2015; Julius et al. 2021).

    Description

    The Asian house rat is a blackish (or brownish) murid rodent of medium size, with a tail that is equal to or longer than its head and body. Adults measure 114–224 mm in body length, 110–231 mm in tail length, 30–43 mm in hind foot length, and 16–25 mm in ear length and they weigh 65–300 g (Stuart et al. 2008). In general, the dorsal fur has a brown hue, although it can also be reddish-brown, greyish-brown or dark brown (Heaney et al. 1998; Aplin et al. 2003). The fur on the belly is mostly whitish. It shares the same morphology with R. rattus, which is its sister taxon (Aplin et al. 2003; Musser & Carleton 2005).

    Getting around

    Asian house rats are fast-moving species with agile movement and strong climbing abilities. They often inhabit ceilings, roofs and wall gaps thus causing damage to human dwellings (Barnett 2001). Most activity takes place early in the evening, usually before midnight, and it can also be spotted during the day in places with high population densities, like urban areas.

     Communicating

    Asian house rats are highly social creatures, and their communication involves olfactory receptors and pheromones, body language/behaviour, and vocalisations. All of these things are an integral part of how rodents coexist with one another (Carew & Ghosh 2020).

    Distribution

    Asian house rats are a native species of southeast Asia (Niethammer & Martens 1975), attained a cosmopolitan distribution through transportation by humans and have introduced to many parts of the world (Musser & Carleton 2005). The native range extends from eastern India through Myanmar, northern Laos and Vietnam to southern China and Taiwan, but populations are now widely distributed across the Indo-Malayan region, including the Philippines (Aplin et al. 2011). In South Africa the presence of R. tanezumi was reported in 13 locations, specifically in four provinces, namely Gauteng, KwaZulu-Natal, Limpopo and Mpumalanga (Bastos et al. 2011). Additionally, Ringani et al. (2022) reported that R. tanezumi was found mostly in inland regions in the provinces of Gauteng and Mpumalanga, as well as along the northeastern and southeastern coast (KwaZulu-Natal and Eastern Cape), and partially in the south (Western Cape).

    Habitat

    Both indoor and outdoor environments are home to Asian house rats, although most pest populations frequent outdoor environments, causing crop damage before harvest (Htwe et al. 2012; Singleton et al. 2004). Asian house rats will migrate to residential regions and even indoor places in search of food after harvest season, resulting in damage to houses (Miller et al. 2008).

    Food

    Asian house rats are omnivorous but mostly consumes plant matter. It is the most damaging rodent pest in rice fields and a major pest of coconut, banana and maize (Stuart et al. 2016).

    SEX and LIFE CYCLES

    Sex:

    Asian house rats reproduce all year long. A litter typically contains three to seven young, born after a short gestation period of around 3–4 days, and at about 15 days old, the eyes open. Infants can begin eating solid food at about three weeks old, are weaned at about one month, and become sexually mature as early as three months. Mature females weigh between 80 and 100 g, while some have indicated that 50 g is the minimum weight (https://www.gbif.org/species/197825678).

    Family life:

    Asian house rats usually live in polygynous groups with multiple males and females and have more than one breeding partner.

    THE BIG PICTURE

    Friends and Foes

    Rattus tanezumi interact with other species in the food chain through various mechanisms, such as trophic interactions (by serving as either prey or predators, they forge new connections that impact the number of local species); direct effects (invading species can influence native populations through bottom-up methods like resource enhancement or top-down methods like predation); indirect effects (by exploitative behaviour and apparent competition, they might have an indirect impact on species that do not directly interact with them); competition (native populations often collapse as a result of competition with invasive species for resources); ecosystem engineering (some alter nutrient cycles or ecosystems, which has an impact on the whole food chain); and mutualisms (by establishing new, advantageous ties with locals, they may change the dynamics of the food web).

    Smart Strategies

    Asian house rats are highly adaptive and omnivorous, they eat just about anything, although they prefer plant to animal foods and readily eat human trash. They are active at night, particularly around dawn and dusk and migrate throughout certain seasons. These rats go to the fields and settle in farms when the spring and fall harvests are ready to be harvested, causing damage to the crops (Miller et al. 2008). They are agile and have strong climbing abilities, and they therefore often inhabit ceilings, roofs and wall gaps, thus causing damage to family living areas (Barnett 2001) 

    Poorer world without me

    Asian house rats play various roles in the ecosystem, including nutrient recycling, seed dispersal, as a food source and indicator species, contributing to maintaining ecosystem balance and diversity (Pimsai et al. 2014).

    People & I

    People always assume that Asian house rats are found only in dirty or unsanitary environments. However, R. tanezumi can thrive in various environments, from rural to urban areas.

    Conservation status and what the future holds

    The IUCN Red List of Threatened Species assessed the Asian house rat in 2016 and they classified it as Least Concern, which means it’s not considered threatened or endangered (IUCN Redlist).

    Throughout its native and introduced distribution range, it is vigorously trapped and poisoned to attempt to control populations, which are increasing across its distribution. There are biosecurity measures in place for tackling the invasive species, for example public education campaigns, as well as early detection and rapid response systems, to remove the species and restore affected habitats (Wood & Chung 2003; Atta et al. 2018).

    Relatives

    Previously, only two invasive Rattus species were known to exist in South Africa: namely, Rattus norvegicus, also known as the Norway rat or brown rat, and Rattus rattus, also known as the black rat, house rat or ship rat (Skinners & Smithers 1990). It’s possible that the three species were inadvertently brought to South Africa and other parts of the world as stowaways on ships (Atkinson 1985; Long 2003).

    Rattus norvegicus is native to eastern Siberia, northern China and Japan, R. rattus to India and southern Asia, and R. tanezumi to southeast Asia, Japan and Fiji (Aplin 2003; Musser & Carleton 2005). While archaeological data from the Iron Age implies that the prevalence of R. rattus may have preceded the arrival of Europeans, R. norvegicus was first documented in South Africa following the arrival of the first European settlers in 1832 (Davis & Fagan 1962; Avery 1985).

    About 15 years ago, a small mammal genetic profiling programme discovered Rattus tanezumi in South Africa, marking the first occurrences of this species on the African continent. (Bastos et al. 2011). It is morphologically similar to R. rattus and was already well established in a number of the nation’s cities as it most likely went unnoticed. The two species belong to the cryptic R. rattus species complex. Genetic profiling, such as cytogenetic and DNA sequencing data, is necessary to differentiate them. R. norvegicus differs morphologically from R. rattus and R. tanezumi due to its somewhat greater body size.

    Scientific Name and Classification:
    Kingdom: Animalia
    Phylum: Chordata
    Class: Mammalia
    Family: Muridae
    Genus: Rattus
    Species: Rattus tanezumi Temminck, 1844
    Common names: Asian house rat, common Philippine field rat, oriental house rat, Tanezumi rat (Eng.)

    References and further reading

    • Aplin, K.P., Chesser, T. & Have, J.T., 2003. Evolutionary biology of the genus Rattus: profile of an archetypal rodent pest. Aciar Monograph Series, 96: 487–498.
    • Aplin, K.P., Suzuki, H., Chinen, A.A., Chesser, R.T., Ten Have, J., Donnellan, S.C., Austin, J., Frost, A., Gonzalez, J.P., Herbreteau, V. and Catzeflis, F., 2011. Multiple geographic origins of commensalism and complex dispersal history of black rats. PloS one, 6(11), p. e26357.
    • Atkinson, I.A.E. 1985. Spread of commensal Rattus to Oceanic Islands and their effect on island avifaunas’, in P.J. Moors (ed.) Conservation of Island Birds: Case Studies for the Management of Threatened Island Species, 3rd ed, pp. 35–81. Cambridge, UK: International Council for Bird Preservation
    • Atta, B., Rizwan, M., Sabir, A.M., Yaqub, M. & Akhter, M. 2018. Field evaluation of rodenticides treated baits for the effective control of field-rats in rice crop. World Journal of Agricultural Sciences 14(5): 137–143.
    • Avery, D.M. 1985. ‘The dispersal of brown rats Rattus norvegicus and new specimens from 19th century Cape Town’, Mammalia 4: 573–577.
    • Barnett, S.A. 2001. The story of rats. Their impact on us, and our impact on them. Crows Nest: Allen & Unwin.
    • Bastos, A.D., Nair, D., Taylor, P.J., Brettschneider, H., Kirsten, F., Mostert, E., Von Maltitz, E., Lamb, J.M., Van Hooft, P., Belmain, S.R., Contrafatto, G., Downs, S. & Chimimba, C.T. 2011. Genetic monitoring detects an overlooked cryptic species and reveals the diversity and distribution of three invasive Rattus congeners in South Africa. BMC Genetics 12: 1471–2156.
    • Carew, S.J. & Ghosh, A., 2020. Shared pheromonal communication of specific fear between adult sprague dawley rats. Bio-protocol 10(6), pp.e3564-e3564.
    • Davis, D.H.S., and Fagan, B.M. 1962. ‘Sub-fossil house rats (Rattus rattus) from Iron Age sites in Northern Rhodesia’, News Bulletin of the Zoological Society of South Africa 3: 13–5
    • Heaney, L.R., Balete, D.S., Dolar, M.L., Alcala, A.C., Dans, A.T.L., Gonzalez, P.C., Ingle, N.R., Lepiten, M.V., Oliver, W.L.R., Ong, P.S., et al., 1998. A synopsis of the mammalian fauna of the Philippine Islands. Fieldiana Zoology new series, 88: 1–61.
    • Htwe, N.M., et al. 2012. Breeding ecology of rice field rats, Rattus argentiventer and R. tanezumi in lowland irrigated rice systems in the Philippines. Agric Ecosyst Environ. 161: 39–45.
    • Julius, R.S., Brettschneider, H., Chimimba, C.T. & Bastos, A., 2021. Prevalence and diversity of the Streptobacillus rat-bite fever agent, in three invasive, commensal Rattus species from South Africa. Yale J Biol Med. 2021 Jun 30; 94(2): 217–226.
    • Keller, R.P., Geist, J., Jeschke, J.M. & Kühn, I., 2011. Invasive species in Europe: ecology, status, and policy. Environmental Sciences Europe 23: 1–17.
    • Kosoy, M., Khlyap, L., Cosson, J.F. & Morand, S., 2015. Aboriginal and invasive rats of genus Rattus as hosts of infectious agents. Vector-Borne and Zoonotic Diseases 15(1): 3–12.
    • Long, J. 2003. Introduced mammals of the world: their history, distribution and influence. Csiro Publishing. Pp. 172–199.
    • Miller, R.W., et al. 2008. Biology and management of rodent communities in complex agroecosystems – rice terraces. In: Singleton, G., Joshi, R., Sebastian, L., (eds). Philippine rats: ecology and management. Luzon: Philippine Rice research institute (PhilRice). Pp. 25–36.
    • Musser, D.E. & Carleton, M.D. 2005. Superfamily Muroidea. Mammal species of the world, Vol. 2 (ed. by D.E. Wilson and D.M. Reeder), pp. 894–1531. The Johns Hopkins University Press, Baltimore, MD.
    • Niethammer, J. & Martens, J. 1975. Die gattungen Rattus and Maxomys in Afghanistan and Nepal. Zeitsch Fur Saugetier 40: 325–355.
    • Pimsai, U., Pearch, M.J., Satasook, C., Bumrungsri, S. & Bates, P.J., 2014. Murine rodents (Rodentia: Murinae) of the Myanmar–Thai–Malaysian peninsula and Singapore: taxonomy, distribution, ecology, conservation status, and illustrated identification keys. Bonn Zoological Bulletin 63(1): 15–114.
    • Ringani, G.V., Julius, R.S., Chimimba, C.T., Pirk, C.W.W. and Zengeya, T.A., 2022. Predicting the potential distribution of a previously undetected cryptic invasive synanthropic Asian house rat (Rattus tanezumi) in South Africa. Journal of Urban Ecology, 8(1), p.juac005.
    • Singleton, G.R., Brown, P.R., Jacob, J.2004. Ecologically-based rodent management: its effectiveness in cropping systems in Southeast Asia. Njas-wageningen Journal of Life Sciences 52: 163–71.
    • Skinner, J.D. & Smithers, R.H.N. 1990. The mammals of the southern African subregion, 2nd edn. University of Pretoria. Pretoria.
    • Stuart, A.M., Prescott, C.V., Singleton, G.R., Joshi, R.C. 2008. Rodent diversity in the lowland agro-ecosystems of the Sierra Madre Biodiversity Corridor, Philippines. Sylvatrop 18:111–126
    • Stuart, A.M., Prescott, C.V. & Singleton, G.R., 2016. Can a native rodent species limit the invasive potential of a non‐native rodent species in tropical agroforest habitats Pest Management Science 72(6): 1168–1177.
    • Towns, D.R. & Daugherty, C.H. 1994. Patterns of range contractions and extinctions in the New Zealand herpetofauna following human colonisation. New Zealand Journal of Zoology 21(4): 325–339.
    • Witmer, G.W., Pitt, W.C. & Howald, G., 2014. Invasive rodent ecology, impacts, and management with an emphasis on the United States. In Proceedings of the Vertebrate Pest Conference (Vol. 26, No. 26).
    • Wood, B.J. & Fee, C.G., 2003. A critical review of the development of rat control in Malaysian agriculture since the 1960s. Crop Protection 22(3): 445–461.

    Author: Rebecca Magoro

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