The red-eared slider is already finding a comfy home in South Africa, posing a threat to endemic wildlife. Rattlesnakes and the like, on the other hand, are likely to meet more aggressive resistance.

In the US, conservation officials are losing the battle against a South African invasion. African rock pythons and Nile monitors have set up home in the Florida Everglades and are preying on indigenous wildlife that has little defence against them.

But this is not one-way traffic. For in the US and in other countries there are species that, if given a chance, would find South Africa to be a comfortable home.

And one of the most worrying of these alien species is already making a regular appearance in botanical gardens across South Africa: the red-eared slider, a terrapin from the US that has long been a darling of the pet trade.

The red-eared slider is illegal to keep in South Africa without a special permit.

But they are still being traded and kept, as herpetologist Dr Cormac Price of the University of KwaZulu-Natal has discovered.

"We have found them predominantly in either botanic gardens or in city parks. Johannesburg, Cape Town, Durban and Pretoria have all had...