The NEMBA Alien and Invasive Species Lists name 8 species of crayfish as potentially invasive in South Africa. The various species hail from North America, Australia and Europe and many are popular in aquaculture. Escapees which form invasive populations can compete against indigenous freshwater species and alter the natural functioning of streams, rivers and dams, potentially displacing or causing the extinction of local species.

Water hyacinth

Water hyacinth (Pontederia crassipes) is South Africa’s most serious aquatic invader. Previously known as Eichhornia crassipes it is now in the genus Pontederia. Fortunately, several highly effective biocontrol agents have been released to combat the rapid growth and spread of this plant. The Centre for Biological Control at Rhodes University have released over 300 000 plant hoppers (Megamelus scutellaris) onto water hyacinth in Hartebeespoort Dam, which as greatly reduced the density.

Water hyacinth thrives in nutrient rich polluted water systems including rivers, dams, and lakes. It is an ongoing problem across many water bodies, especially in summer when this floating herb can double its growth rate every two weeks.

Tall Verbena

One of three Category 1b invasive plants, purple-top (Verbena bonariensis) is also called tall verbena. It is a common and widely distributed weed that infiltrates grasslands and wetlands. It is a problem in nature reserves and national parks where the seeds are easily spread. It is unpalatable to many indigenous grazing mammals. The purple clustered flowers are prominent in late summer and early autumn.

Tree of heaven

Native to China, the Tree of Heaven (Ailanthus altissima), is an alien invasive tree in South Africa.

It is a common urban invader and generally occupies disturbed areas. Its leaves, flowers and seeds are present during spring and summer. Leaves have a characteristic notch at the base of each leaf and leaves emit a distinctive smell when crushed.

Lyriche Drude from the University of the Witwatersrand is undertaking a study on the distribution of this species. You can assist with this project by providing locality information to the following platforms. If seen at any locality (e.g., roadside or garden), please collect the following:

  • Exact (GPS) location
  • Picture of plant (if possible)
  • Send information to Lyriche Drude at wits@gmail.com



The daisy family has many invasive species including the notorious pompom weed. Another invasive flower of grasslands is the tickseed which comes from the eastern parts of the United States. Like other members of this group, they produce copious numbers of seeds which are easily spread via wind and water.

Spear thistle

A familiar garden and agricultural weed which dominates in some areas during late summer. Spear thistle invades roadsides, seepage zones, grassland and agricultural fields. The leaves are spiky and hairy and therefore unpalatable to livestock and grazing game animals. It can also cause skin irritations to people coming in contact with this weed.

Rose-ringed parakeets

Rose-ringed parakeets are highly sought after and valued aviary birds. Unfortunately, escapees have naturalised in parts of Gauteng and KwaZulu-Natal. They can form large flocks which are destructive to agricultural plants such as maize and sunflower. They feed on and damage commercial fruits and nuts. Parakeets nest in tree holes and cavities and therefore compete against indigenous birds which use the same nesting cavities.

These parakeets are listed under NEMBA Category 2, meaning that a permit is required to keep and breed them in South Africa. Unpermitted and feral rose ring parakeets in nature revert to Category 1b and need to be removed under the NEMBA AIS legislation.

For further information and advice regarding permits and keeping rose-ringed parakeets, contact the Parrot Breeder’s Association (PASA) at the following emails: pvsa@aviculturesa.co.za or pvsa.admin2@aviculturesa.co.za

Red-eared slider

Durban / eThekwini is a subtropical port city and is a hotspot for alien animal and plant invasions. Rose-ringed parakeets are prolific across many suburbs and red-eared slider terrapins are frequently discovered lurking in dams, parklands and waterways…discarded as unwanted pets. They feature in the top 100 list of impactful alien invasive species and pose a threat to our indigenous terrapins and endemic wildlife.

Red sunflower

The red sunflower (Tithonia rotundifolia) flowers from February through to July. It can be abundant along road verges but also penetrates seepage zones and wetlands. It is an annual herb with a rapid growth rate. Although called the red sunflower, the petals are more of a bright orange-red. These images were taken alongside the freeway leading into Pretoria with the iconic UNISA building in the background. Red sunflower is found across Gauteng, Limpopo, Mpumalanga and KwaZulu-Natal.

Red Sesbania

This is a deciduous shrub or small tree reaching 4 metres high. It produces orange or red flowers in late summer and four-winged, elongated seed pods. The seeds are reportedly poisonous to indigenous birds. It is highly invasive along streams and rivers, growing along banks, as well as roadsides and drainage lines in high rainfall regions.