House crows (Corvus splendens) are problematic invasive birds as they associate strongly with informal settlements and industrial areas. They are bold and intelligent and can become aggressive towards children, stealing their food. They also quickly snatch food from street traders. Because they live near people, their droppings may fall onto food items when perched above tuckshops and vendor stands, thereby transmitting enteric diseases to people.
House crows are under management by the City of Cape Town and the population is extremely low due to active intervention. However, there is always a risk of new arrivals coming in by passing ships.
House crows (Corvus splendens) are problematic invasive birds as they associate strongly with informal settlements and industrial areas. They are bold and intelligent and can become aggressive towards children, stealing their food. There are two hotspots for these birds in KwaZulu-Natal – around Durban / eThekwini and around Esikhawini on the outskirts of Richard’s Bay. Authorities have been removing nests, but nests are difficult to access as they are often built high up in trees.
You can report sightings of house crows on the platform: www.inaturalist.org
The Himalayan tahr established on Table Mountain from some zoo escapees in the 1930s. Their population increased exponentially and research into their diet and environmental impacts were undertaken. It was found that an increased population would impact negatively on vegetation and biodiversity in Table Mountain National Park, including soil and rock erosion. They were also competing against indigenous klipspringer. A culling operation was initiated and today there are only a handful of tahr left which are under active management.
Harlequin lady beetle
The harlequin lady beetle is a predatory beetle which outcompetes indigenous ladybeetles and other insects and is known to taint agricultural crops, including grapes. This orange to red beetle has scattered black spots on its wings and a black W or M shape on a white pronotum (neck area). This beetle is found in Asia and was first detected in South Africa around 2001. They have now spread across most parts of South Africa.
The giant milkweed (Calotropis procera) is used for fibre and medicine, but it rapidly invades subsistence agricultural fields. Parts of the plant is poisonous if eaten by livestock. It thrives in the hot northern regions of Limpopo Province.
A soft woody shrub attaining 2 metres in height, they produce large oval fruits. This plant is also found along road verges and in drainage lines.
Famine weed (Parthenium hysterophorus) is one of Africa’s most serious invasive plants as it displaces subsistence farmers in rural areas. It is a fast-growing annual herb reaching 1,5 metres in height. It thrives in warm climates with heavy rainfall and will quickly outgrow and smother subsistence crops. Some invasions are so bad that people have to vacate their land.
Famine weed also produces skin irritant chemicals and allergens which can have a detrimental effect on people who must work in their fields. Livestock grazing on famine weed develop mouth ulcers and body deterioration. It also taints the milk.
European shore crab
The European shore crab is also known as the green crab. It has become a nuisance animal in ports and docks around Cape Town. They are found in Table Bay and Hout Bay.
An evergreen shrub reaching two metres in height. Thrives in shaded areas of forests and vegetated river courses. The fruits turn from a pale green to a coral red.
Common thorn apple
The common thorn apple (Datura stramonium) is widespread across the country. It produces copious amounts of tiny black seeds which are dispersed by water runoff. All parts of this plant are toxic to livestock. This plant is prolific during summer and invades roadsides and agricultural land, as well as dump sites.
Bugweed (Solanum mauritianum) is a large shrub growing 2-4 metres high with spreading branches and large, velvety leaves. It has a somewhat pungent smell. Despite the unripe fruits being poisonous, many birds and some mammals like duiker and monkeys will feed on the ripe fruits. Seeds are dispersed widely in this manner. Bugweed should be removed from your garden the moment it is detected, as it is easier to control small shrublets before they grow too large.