Australasian Science: Australia's authority on science since 1938

The Illegal Wildlife Trade as a Source of New Alien Species

This red-eared slider turtle (Trachemys scripta elegans) was found in Adelaide in 2016, despite being banned in Australia. Credit: Pablo García Díaz

This red-eared slider turtle (Trachemys scripta elegans) was found in Adelaide in 2016, despite being banned in Australia. Credit: Pablo García Díaz

By Pablo García Díaz, Joshua Ross, Andrew Woolnough & Phill Cassey

The illegal wildlife trade is increasing the likelihood that foreign reptiles will become established in the wild – with consequences for both biodiversity and human health.

Two of the processes most threatening biodiversity – the illegal wildlife trade and the introduction of alien species – can intersect with potentially negative effects. Our investigation of illegal reptile-keeping in Victoria found that 12 of the 28 reptiles known to be kept illegally could become established and form self-sustaining breeding populations in the wild.

Moreover, our research indicates that the keeping of illegal reptiles in Victoria is not only a likely environmental issue but also a potential human health hazard. Of the 28 illegal reptiles reported in our study, ten of them are highly venomous snakes that aren’t native to the country.

The Risk Posed by Illegally Kept Reptiles

There is a blanket ban on importing and keeping alien reptiles in Australia. This may have the unintended consequence of fostering the illegal trade in reptiles, as species that are rarely available may become more sought-after by wildlife enthusiasts.

Victorian authorities have been conducting a long-running campaign to seize illegal species within the state. Strategies have included an amnesty for people to relinquish alien species, and active policing efforts to seize illegally kept reptiles.

Our investigation gathered information about alien reptile species reported in the state during the period 1999–2012, and this gave us an insightful snapshot of the diversity of alien reptiles present within the borders of the state. We then used this information to evaluate the risks posed by illegal reptile-keeping in Victoria.

The first step in our research was to understand historical patterns of reptile establishment success in mainland Australia and the island territories of Christmas Island, the Cocos (Keeling) Islands and Lord Howe Island over the period 1840–2005. We asked:

  • which alien reptile species have been introduced in the past (i.e. ever been found in the wild in Australia)?
  • of those introduced, which ones are established in Australia?
  • are there any differences between the species that were successful and those that failed to establish?

Comparing the features of failed and successful alien reptiles through a statistical model provided insights into the factors determining the establishment success of alien reptiles in Australia. Our results revealed that successful alien reptiles were smaller in body length and were released or escaped a higher number of times into the wild than their failed counter­parts. Both factors have influenced the establishment success of alien reptiles in other parts of the world.

Once we had constructed a model for predicting the establishment success of alien reptiles in Australia, we proceeded to estimate the risk of establishment of the 28 illegally kept reptile species in Victoria. We used a statistical model based on historical species introductions to predict what will happen if the illegally kept reptiles are released in mainland Australia.

Moreover, our research indicates that the keeping of illegal reptiles in Victoria is not only a likely environmental issue but also a potential human health hazard. Of the 28 illegal reptiles reported in our study, ten of them are highly venomous snakes that aren’t native to the country.

Our findings indicated that the probability of illegal reptiles becoming established varied across species. The most likely introduced reptiles to become established successfully were the American common snapping turtle (Chelydra serpentina), with a 70% chance of establishing, the Asian Burmese python (Python bivittatus, 59%), the South American yellow anaconda (Eunectes notaeus, 57%) and the African puff adder (Bitis arietans, 56%).

These four species are examples of an existing motivation to keep reptiles illegally despite the potential for serious conservation consequences if they become established in Australia. For example, the invasion of the Florida Everglades by Burmese pythons is devastating this valuable ecosystem, with pythons being identified as the cause of the decline of mammals. In its native African range, puff adder bites are considered to be the greatest cause of human deaths due to snake envenomation.

Considering the 28 illegally kept species altogether, our analysis revealed that 12 (42.9%) of these reptiles may become established in Australia if they are released at least three times.

Collaboration and Information

The illegal trade in wildlife and the invasive spread of alien species are textbook cases of a so-called “wicked” problem in conservation biology, where social, ecological and economic dimensions are entwined in a complex manner that makes successful interventions difficult at best and almost impossible to resolve at worst. As if their independent effects were not sufficiently challenging, our research suggests a synergy between the two threat processes, with the illegal wildlife trade being a potential pathway for alien species.

The transnational nature of the illegal wildlife trade in alien reptiles calls for multilateral cooperation between exporting and recipient localities. Implementing such an approach requires additional knowledge and research for improving our understanding about where the illegal reptiles originate in the trade chain. In Australia we recommend more public awareness campaigns to reduce the demand for alien pets and illegal wildlife.

This tangled web of science, policy, regulation and enforcement requires collaboration, support and ingenuity to avoid the establishment of more alien species in Australia.


Pablo García Díaz is a PhD candidate at The University of Adelaide’s Invasion Ecology Group. Joshua Ross is a mathematician in the School of Mathematical Sciences at The University of Adelaide. Andrew Woolnough works on invasive species management with the Victorian Department of Economic Development, Jobs, Transport and Resources. Phill Cassey leads the Invasion Ecology Group at The University of Adelaide's Environment Institute.