House crows were introduced to South Africa in the 1970s. (Photo by Tobias SCHWARZ / AFP)
The last two years have been remarkable. The lockdown periods, restrictive for us humans, allowed many species to start moving around without our interference. Scientific literature is full of examples of birds and mammals that were seen in cities where they are normally absent or rare.
While these unusual sightings delighted us from our locked-down positions, another set of animals was also taking advantage of this time.
Programmes controlling invasive species, like so many other things, were suspended during lockdown. However, the animals and plants themselves had no such inhibitions. They may even have been able to move and invade areas faster than they would otherwise be able to.
Here are some invasive animals to look out for in 2023.
House crow
Native to the Indian subcontinent, house crows were introduced to South Africa in the 1970s. Populations were established in Durban and then Cape Town and have remained there for nearly 50 years. In the past five years, though, these clever animals have been spreading along the coast to many new towns, such as Richards Bay and East London. They have even hitched rides on lorries to appear in some of our inland areas (such as Howick).
During lockdown, populations established in new localities, including Gqeberha. Watch out for house crows near you. They are distinctive from native crows in that they are smaller and all black with a grey hood. They are a particular problem near rubbish dumps and have been known to attack people carrying food, including children in playgrounds. But other invasive populations are known to carry diseases (including salmonella) and have significant impact on native songbirds.
Domestic pig
Domestic pigs have been in South Africa for more than 9 000 years but populations have been deliberately introduced into the wild a number of times as biological control against the emperor pine moth. Recently, feral pigs have been spotted in new locations around the country, especially in the lowland areas of the Western Cape.
It is possible the growth in demand for free-range pork has resulted in animals escaping from captivity. These feral pigs have the potential to carry disease both to domestic stock as well as native warthogs and bush pigs. In addition, feral pigs will eat tortoises and dig up bulbs.
Red swamp crayfish
For 22 years the only population of red swamp crayfish in South Africa was hanging on at a small facility near Dullstroom in Mpumalanga. But a couple of years ago a new population was reported from a small dam near Welkom in the Free state.
Now another population has been found near Vredendal in the Western Cape associated with both the Olifants River system and a significant irrigation network.
(Photo by Odd ANDERSEN / AFP)
The red swamp crayfish is not the only invasive species here as we also have an Australian species called the red claw crayfish, which is found in large areas of Mpumalanga and is spreading into KwaZulu-Natal, eSwatini and Mozambique.
These species are especially bad in South Africa as there are no native freshwater crayfish here. Invasive populations elsewhere are known to cause great ecological disturbance, as they burrow into the banks of dams and rivers. In South Africa they may impact negatively on our native crabs as well as carrying novel parasites.
Rose-ringed parakeet
Perhaps one of the prettiest of South Africa’s invasive species, the rose-ringed parakeet was introduced because it was a popular caged bird. It is not only invasive here but in 35 countries on five continents. These birds were already common in Durban by the 1970s but have been increasing their range, particularly in urban areas, so that the Durban population now covers 730km2.
(Photo by PRAKASH SINGH / AFP)
You are likely to notice this bird as it makes a lot of noise when flying around. It impacts other cavity nesting birds by competing for nesting sites. It is also a pest for some agricultural crops and spreads diseases. Many people still want to keep these birds as pets, which is possible with a permit.
Common dwarf gecko
Have you seen geckos moving around in the day when they used to move around only at night? We are all familiar with geckos in South Africa but this is the only species that you will see moving around in the daytime. The first records of alien populations of the common dwarf gecko date back to the 1950s. This is a species that naturally occurs in northeastern areas of South Africa, and it is easily accidentally transported with things like firewood and nursery plants because they stick their eggs in dry places.
In the past 10 years populations have been spreading very rapidly in many urban areas around the country. There have been very few studies done so far and so we do not know whether they have any serious impact on their new environment.
If you spot any of these invasive animals, or any other animals or plants that you suspect are invasive, please report them at invasives.org.za. If you can take a picture you can place it on a citizen science platform like iNaturalist (inaturalist.org). Otherwise inform your local conservation authority or the South African National Biodiversity Institute.
Invasive species can do a lot of harm but we can only tackle them if we know what they are and where they are. So we rely on you to help us.
You can read more about the invasive animals of South Africa at https://doi.org/10.1007/978-3-030-32394-3_5
John Measey is a researcher at the Centre for Invasion Biology at Stellenbosch University.