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Invasive plants and animals: Terrestrial animals


Andrew Wilke and Alexsis Wilson, Department of Primary Industries and Fisheries


Tony Pople, Department of Primary Industries and Fisheries

Key findings

  • Pest animals cost Queensland at least $110 million a year by preying on livestock, causing crop losses, competing for pasture and spreading disease. They also have uncosted impacts on the environment through overgrazing, predation, competition and poisoning.
  • Pest animals can be a nuisance in urban areas, where they spread disease and can be traffic hazards.
  • Most exotic vertebrate pests have long been established in the state and have broad distributions. Eradication is not feasible for these species, so their management must focus on restricting their spread, preventing new introductions and controlling their impacts.
  • Control needs to be sustained and well coordinated and target areas of high actual or potential impact.
  • One national and five state strategies are implemented to manage pest animals in Queensland.
  • Increased transport of people and goods will continue to test border security.
  • Recent introductions include three tramp ant species, for which eradication is being attempted. The pet trade is another source of introductions despite legislation prohibiting the keeping of likely invasive animals as pets.
  • New control methods are being developed as there is an increasing need for techniques that are humane, target-specific and cost-effective in reducing the impacts of pests.

Indicators and summary of status


Status of indicator

Current and potential extent, density and distribution of pest animals

Exotic terrestrial vertebrates are widespread throughout Queensland, and some species (such as wild deer and feral horses) have the potential to expand their range. Exotic birds are currently patchily distributed and have significant potential to expand.

Impacts on assets

Pest animals cost Queensland, conservatively, $110 million a year. Feral pigs and wild dogs alone cost $45 million a year in lost primary production. Pest animals are also responsible for unmeasured environmental and social costs.

Number of local governments with pest management plans

At 30 June 2007, 119 of Queensland's 157 local governments have endorsed pest management plans in place.

Number of biological control agents released

Release of rabbit calicivirus for the control of wild rabbit populations continues. No new biological control agents have been released for vertebrate pests.

Implementation of pest animal strategies

An Australian Pest Animal Strategy has recently been developed and is implemented in Queensland.

State strategies include the Queensland Pest Animal Strategy and strategies concerning feral pigs, locusts, mice and rabbits.

Local Government Area Pest Management Plans and Natural Resource Management Plans are also currently implemented.

Introduced species

Multiple incursions of yellow crazy ants (Anoplolepis gracilipes) have occurred in Queensland since 2001. Electric ants (Wasmannia auropunctata) were detected in 2006.

Species outbreaks

Isolated mouse outbreaks and one locust plague have occurred in Queensland
since 2003.


Environmental impacts

Introduced pest animals place considerable pressure on native plants and animals. Negative environmental impacts include:

  • direct predation on native fauna. Foxes (Vulpes vulpes) and feral cats (Felis catus) have been implicated in the decline and, in some cases, the extinction of at least 17 native species;
  • overgrazing, leading to land degradation and a reduction in water quality;
  • destruction of native plants that provide food and shelter to native species;
  • competition with native animals for food and shelter; and
  • poisoning of native animals and spreading of disease. The decline in abundance of native predators has been attributed to poisoning by cane toads (Bufo marinus).

Some pest animals affect specific habitats or species, while others have more general impacts, affecting many species, whole ecosystems and underlying ecological processes. Currently, feral pigs (Sus scrofa) damage several habitat types, including World Heritage-listed rainforest, displace the already endangered cassowary (Casuarius casuarius) (McGaw and Mitchell 1998), and destroy up to 100% of marine turtle eggs on some nesting beaches (Cape York Peninsula Development Association 2007).

Economic impacts

Pest animals reduce the viability of primary industries, which account for a significant proportion of Queensland's export income:

  • feral pigs cost $12 million in reduced grain production in 1996 (McGaw and Mitchell 1998);
  • wild dogs (Canis familiaris) cost an estimated $18 million a year in sheep and cattle losses from predation and a further $9 million associated with the spread of diseases such as hydatidosis and Neospora caninum. Control costs approximately $5.4 million (DNRM 2004); and
  • in the mid-1990s mouse (Mus domesticus) plagues cost an estimated $3-18 million in lost agricultural production and $0.4-1.2 million in costs to landowners for control (Caughley 1998).

The economic value of some impacts of pest animals-for example, environmental and social impacts such as decreased biodiversity or predation on pets-is difficult to estimate.

Social impacts

Pest animals can lower the cultural and aesthetic value of the natural landscape and pose a risk to human health.

Negative social impacts include:

  • potential and actual disease transmission;
  • predation of, and attacks on, domestic poultry, stock and pets;
  • traffic hazard (for example, from feral horses and wild deer);
  • reduction in the community's enjoyment of natural areas;
  • general nuisance in urban areas; and
  • damage to cultural sites.

The social impacts of pest animals are most obvious in urban areas, where they are most likely to come into contact with people; for example, deer pose a hazard to motorists (O'Keefe and Walton 2001).

Pressure and condition

Pathways of introduction

Most pest animals in Queensland were introduced at the time of European settlement for food, sport and aesthetic value. Today, introductions of pest animals are most likely to occur illegally through the pet trade and for hunting purposes, or unintentionally through transport of goods and people.

Queensland has a list of prohibited pets, which includes all declared animals such as the rabbit (Oryctolagus cuniculus) and ferret (Mustela furo). Prohibited pets are animals that are already, or have the potential to become, established pests in Queensland.

The small size of invertebrates increases the chance of their accidental introduction by the transport of people and goods. Yellow crazy ant (Anoplolepis gracilipes) incursions are most commonly associated with areas where shipping containers are unloaded and cleaned. However, pest ant species can be spread by the translocation of products such as soil, pot plants, camping equipment and mulch.

Obstacles to pest management

Debate over whether an animal is a pest can delay the implementation of control measures. Large exotic mammals such as pigs, goats (Capra hircus), horses (Equus caballus), camels (Camelus dromedarius) and the four deer species (Axis axis, Cervus elaphus, Cervus timorensis and Dama dama) that have established in Queensland may be valued commercially, aesthetically or for game hunting.

Reinvasion by pest animals from areas where harvesting or baiting has occurred can negate control efforts. Consequently, an integrated management approach, broad-scale control methods and coordinated efforts are essential for pest animal management.

Suitable control methods for pest animal management may be opposed on the grounds that they are inhumane or not target-specific. Much effort has been invested over the past 20 years to refine the use of pesticides and traps to minimise such side effects.

Declared pest animals

All exotic mammals, reptiles and amphibians are declared as Class 1 pests in Queensland under the Land Protection (Pest and Stock Route Management) Act 2002 (Qld). Exceptions are six species that are specifically identified as Class 2 pests under the Act and a set of 32 non-declared species, which are mostly domestic animals or species for which there are no broad-scale control measures, such as cane toads. Three native locusts (Chortoicetus terminifera, Austracris guttulosa and Locusta migratoria) that form plagues are declared as Class 2 pest animals and the exotic yellow crazy ant is declared as a Class 1 pest. Landholders, including local governments and state agencies, are required to control Class 1 and 2 pests on their land. It is an offence to introduce, keep, feed or release a declared pest animal without a permit.

Table 8.1 shows a selection of declared and non-declared terrestrial vertebrate pests established in Queensland. Birds are listed separately as they are not covered by the Act. The current and potential distributions of terrestrial vertebrates and birds are shown collectively in species richness maps in Figures 8.1-8.4. The maps show that there is potential for spread for birds, but comparatively little for terrestrial vertebrates, with the exception of wild deer. The terrestrial vertebrates in Table 8.1 currently occupy an average of 54% of their potential range in Queensland. Each species on average occupies about 48% of the blocks in the state, but this could expand to 82%. Exotic birds currently occupy an average of 13% of their potential range. The potential distribution of the exotic birds listed in Table 8.1 shows that areas of western Queensland that currently have two or fewer species could eventually have all species present.

This contrast between taxonomic groups has been extended to exotic weeds and freshwater pests in Figure 8.5, highlighting the fact that weeds, fish and birds have greater scope for expansion than exotic mammals.

Invasive animals

Queensland has 19 mammal, 13 bird, 18 fish (see 'Freshwater plants and animals', page 275), three reptile and one amphibian species that are naturalised.

Invasive insects have become a concern more recently. Three tramp ant species-red imported fire ants (Solenopsis invicta), yellow crazy ants (Anoplolepis gracilipes) and electric ants (Wasmannia auropunctata)-have been detected in Queensland in the past decade.

The giant African snail (Achatina fulica) can feed on over 500 plant species, making it a serious agricultural and horticultural threat. It is renowned for hitchhiking in a variety of cargo types, so high-risk shipping containers are targeted by the Australian Quarantine Inspection Service.

Exotic birds are also a current concern because they are not subject to specific pest legislation in Queensland. Eleven bird species are listed as prohibited wildlife in Queensland under the Nature Conservation Act 1992 (Qld). Red-vented bulbuls (Pycnonotus cafer) and common blackbirds (Turdus merula) are present in Queensland in low numbers in Mackay and Toowoomba. Six exotic bird species are listed by local governments in their Local Government Area Pest Management Plans.

One of the major threats posed by exotic species is the introduction of new diseases. Queensland is currently free of 13 of the worst diseases, which include foot-and-mouth disease, rabies, mad cow disease and avian influenza. In 2005, the Asian tiger mosquito (Aedes albopictus) was found in the Torres Strait islands off the northern tip of Queensland. This exotic species can transmit dengue fever and has a history of invasion, even into colder climates (Russell et al. 2005). The Commonwealth and Queensland Government health departments began a control program for the Asian tiger mosquito in 2005.


 Common name

Scientific name
Table 8.1 A selection of established exotic terrestrial vertebrates and birds in Queensland

Class 2 pests

Wild dog

Canis familiaris

Feral goat

Capra hircus

Feral cat

Felis catus

European rabbit

Oryctolagus cuniculus

Feral pig

Sus scrofa

European fox

Vulpes vulpes

Non-declared animals

Chital deer

Axis axis

Cane toad

Bufo marinus

Red deer

Cervus elaphus

Rusa deer

Cervus timorensis

Fallow deer

Dama dama

Feral horse

Equus caballus

Exotic birds

Common myna

Acridotheres tristis

Mallard (incl. black duck hybrids)

Anas platyrhynchos

Cattle egret (natural invasion)

Ardeola ibis

European goldfinch

Carduelis carduelis

Rock dove (feral pigeon)

Columba livia

Nutmeg mannikin

Lonchura punctulata

Helmeted guineafowl

Numida meleagris

House sparrow

Passer domesticus

Indian peafowl

Pavo christatus

Common pheasant

Phasianus colchicus

Red-whiskered bulbul

Pycnonotus jocosus

Spotted turtle dove

Streptopelia chinensis


Streptopelia decaocto

Common starling

Sturnus vulgaris

Common blackbird

Turdus merula

Source: DNRW

Figure 8.1 Current distribution of established exotic terrestrial vertebrates in Queensland
Source: DNRW

Figure 8.2 Potential distribution of established exotic terrestrial vertebrates in Queensland
Source: DNRW

Figure 8.3 Current distribution of established exotic birds in Queensland
Source: DNRW

Figure 8.4 Potential distribution of established exotic birds in Queensland
Source: DNRW

Figure 8.5 Proportion of the potential range currently occupied by exotic species in Queensland
Source: DNRW

Overabundant native species

Overabundant native species, such as kangaroos, wallabies, possums, rats and birds, can be pests in Queensland. The Nature Conservation Act 1992 (Qld) recognises that native wildlife can sometimes pose a threat to primary production or human health and it is therefore necessary to take wildlife and minimise these occurrences. The Environmental Protection Agency can issue permits allowing native pests to be taken or culled.

Three species of kangaroos are also commercially harvested in Queensland in numbers far greater than the non-commercial cull: 0.5-1.9 million a year over the period 1975-2005. Annual quotas are set at 10-20% of population size, but these are not always met. This harvest will reduce population size, providing some level of damage mitigation to graziers and crop farmers.

Plague species

House mouse plagues reduce profits to cropping industries and constitute a serious nuisance in homes, buildings, and pig and poultry farms. Landholders and governments must expend considerable effort and cost to combat them. Baiting can cost-effectively prevent damage; an average cost:benefit ratio across landholders of 12:1 was reported for the 1997 plague in central Queensland (Caughley 1998). Four species of native rats-the canefield rat (Rattus sordidus), grassland melomys (Melomys burtoni), pale field rat (Rattus tunneyi) and long-haired rat (Rattus villosissimus)-also have population outbreaks.

Locust plagues develop as a result of favourable seasonal conditions. In such conditions, locusts can increase their population per generation up to tenfold. An outbreak of Australian plague locust in 1984 cost approximately $5 million in crop losses. Without locust control, over $100 million of crop losses could have occurred. More recently, an economic analysis of Australian plague locust control (1999-2004) showed a cost:benefit ratio of approximately 1:8.


Pest animal strategies

An Australian Pest Animal Strategy has recently been developed and is implemented in Queensland. It will help coordinate the management of the impacts of vertebrate pests by many stakeholders across Australia. In Queensland, statewide strategies have been implemented for wild dogs, feral pigs, mice, locusts, rabbits and pest animals in general.

At a local scale, at 30 June 2007, 119 of Queensland's 157 local governments had endorsed pest management plans that deal with pest issues specific to their area. Fourteen regional Natural Resource Management (NRM) bodies and various regional pest management groups improve the efficiency and effectiveness of local government plans by aiding coordination, as most pest problems cross local government boundaries.

In February 2005 a Memorandum of Understanding (MoU) for the management of wild dogs inside the wild dog barrier and check fences (other fences that do not link up with the wild dog barrier, but protect animals in the adjacent cropping and grazing land) came into effect between the Department of Natural Resources and Water (DNRW), AgForce Queensland, the Darling Downs Local Government Association, the South West Queensland Local Government Association and the Environmental Protection Agency (EPA). An important component of wild dog management is the Wild Dog Barrier Fence, which is approximately 2500 km long and is estimated to provide a benefit of $3.10 for every dollar invested (EconSearch 2000).

The Blueprint for the Bush was announced in 2006 and is a ten-year plan involving a partnership between the Queensland Government, AgForce Queensland and the Local Government Association of Queensland. Reclaim the Bush, a Pest Offensive is an initiative under Blueprint for the Bush, which will contribute $11 million over the next four years to tackle weeds and pest animals.

Tramp ant eradication

Eradication programs are currently under way in Queensland for three tramp ant species. The yellow crazy ant program is managed by DNRW and control measures at a number of sites have significantly reduced numbers of this species.

An Electric Ant Control Centre involving the Department of Primary Industries and Fisheries (DPI&F), DNRW and the EPA was established in 2006. The centre's activities include surveillance and treatment, controls on movement of goods, engaging the community in education and awareness, and assessment of treatment and surveillance methods.

The red imported fire ant eradication program was initiated by DPI&F in 2001. Only isolated colonies remain, but detection becomes harder as density is reduced and less prominent colonies remain.

Research and education

Cost-effective, humane and target-specific control methods for animal pests are the ideal. Researchers are currently investigating alternative feral pig toxins (Cowled et al. 2006), trapping strategies for feral pigs in tropical rainforests, the potential use of baits to carry vaccines and contraceptives, and alternative rodenticides.

In 2005-06, a three-year, $1 million research initiative on cane toads began through the Institute of Molecular Bioscience at The University of Queensland and the Invasive Animals Cooperative Research Centre to better understand the chemical ecology of cane toads. Armed with this knowledge, researchers hope to develop synthetic chemicals specific to cane toads to improve baiting and trapping programs, disrupt breeding or render the toads vulnerable to predators.

Government extension officers play an essential role in the distribution of research and education to landholders and other stakeholders, which leads to the practical application of pest animal prevention and control. The reciprocal communication between extension officers and landholders is also useful in pre-empting and overcoming problems with control methods and education.

Pest Patrol, an education program for young primary school students, raises awareness of the dangers posed by pest animals to native wildlife. Such education programs are important to ensure that people have the skills and knowledge needed to make informed decisions regarding pest animals and to provide pest animal experts in the future.


Cape York Peninsula Development Association 2007, Turtle Nest Monitoring Project Report July-December 2006, unpublished report to Environment Australia, Canberra.

Caughley, J. 1998, House mouse (Mus domesticus) in Queensland, Department of Natural Resources, Brisbane, viewed 6 January 2007,

Cowled, B.D., Gifford, E., Smith, M., Staples, L. and Lapidge, S.J. 2006, 'Efficacy of manufactured PIGOUT® baits for localised control of feral pigs in the semi-arid Queensland rangelands', Wildlife Research 33: 427-437.

DNRM 2004, Economic assessment of wild dogs, Rural Management Partners, Department of Natural Resources and Mines, Brisbane.

EconSearch 2000, Economic assessment of the wild dog barrier fence, report to the Department of Natural Resources, Brisbane.

McGaw, C.C. and Mitchell, J. 1998, Feral pigs Sus scrofa in Queensland: pest status review series, Department of Natural Resources and Mines, Brisbane, viewed 17 January 2007, pdf.

O'Keefe, M.S. and Walton, C. 2001, Vertebrate pests of built-up areas in Queensland: pest status review series, Department of Natural Resources and Mines, Brisbane, viewed 8 January 2007,

Russell, R.C., Williams, C.R., Sutherst, R.W. and Ritchie, S.A. 2005, 'Aedes (Stegomyia) albopictus-a dengue threat for southern Australia?', Communicable Diseases Intelligence 29: 296-298.

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Last reviewed
18 May 2011
Last updated
13 February 2008