ASI Newsletter - May 2019 

Hitchhiking Snakes

Reptile distributions are relatively well known in South Africa and we have had decent, and for the most part, accurate distribution maps for at least the last fifty years. Due to this, we have a good understanding of where most species of reptiles occur. Snakes in particular, being generally large and charismatic, are well documented from around the country. When a farmer comes to tell us of the Green Mamba he shot on his farm in Thabazimbi, we can, with a certain level of confidence, suggest that it was more than likely a Boomslang, as Green Mambas are restricted to the coastal forests of KwaZulu-Natal in South Africa and do not occur in Limpopo.

However, occasionally we see snakes pop up in areas where they should not occur. Sometimes it may just be that their distribution was somehow overlooked (for example the presence of Black Mambas in the Northern Cape) or the snake has been moved into this area unintentionally by humans. We call this hitchhiking.

A Green Mamba recently seen in one of the rest camps in Kruger National Park. With around 1500 people entering the park each day during the holiday season, it's surprising we don't see more hitchhikers in the park and camps. (Photo supplied by Barry Greenshields)

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Hitchhiking occurs when a snake is transported from one area to another, usually as a stowaway with cargo such as plants, hay bales, fire wood or any semi-natural product that snakes can hide in. The snake then gets off the vehicle at a new location, often hundreds of kilometres away. These snakes will most likely not survive as the new habitat and climate may be too harsh or unsuitable. Quite often these hitchhikers end up in suburbia or industrial areas

A Mozambique Spitting Cobra hitchhiking in a bag. 

Hitchhiking is not common if you compare the number of trade routes in South Africa and the number of transport vehicles that move around the country daily. Although we cannot confirm the number of hitchhikers as they are seldom observed exiting from vehicles, we don’t see too many reported cases. If a species is moved within its range, we cannot know if it is local snake or a hitchhiker. A Brown House Snake found on a truck in Gauteng, coming from the Western Cape, may be a hitchhiker, or it may be a local snake that climbed onto the truck whilst it was parked overnight somewhere in Gauteng. We do however suspect a Black Mamba caught in Johannesburg is a hitchhiker as the closest known distribution records are from northern Pretoria - around 80 km away. The habitat around Johannesburg is vastly different from that of Pretoria North and unsuitable for Black Mambas..

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Another aspect is that the snake may not be a hitchhiker at all, but rather an escapee. We know the keeping of snakes is a large industry in South Africa and sometimes things go wrong. For example, we have seen a Mozambique Spitting Cobra caught in Grahamstown, Eastern Cape, around 400km away from the closest known distribution. But it turns out that a known snake keeper lives on the same street the snake was caught. A couple of years ago, a snake remover caught a Western Diamondback Rattlesnake in a garden in Bryanston, Johannesburg. A Coral Shield Cobra was caught in an urban garden in Amamzimtoti. And one of the most popular snakes in the pet trade, the American Corn Snake, is removed from suburban gardens almost weekly by snake removers around the country. These are without a doubt snakes that have escaped from a collection. Generally, you can tell a captive snake, even if it is a local species, apart from wild ones. They will be overfed and clean without any scars. This form of facultative hitchhiking is a serious problem as ‘hitchhikers” can be venomous exotic species that we don’t have antivenom for in South Africa.

White Lipped Tree Vipers are probably one of the most common exotic venomous species in the pet trade and we see a number escaping and being removed by snake removers in urban areas. 

This movement of exotic or pet snakes has caused some invasions in certain parts of the world. The well-known cases of this are the Brown Tree Snakes of Gaum, accidentally brought in by the American military in cargo, and now established and invasive on the island and threatening many endemic bird species. The Burmese Python in the Everglades in America is also well known and causes problems. South Africa has its own invasion, namely the Flowerpot Snake or Brahminy Blind Snake known from around Durban and Cape Town and brought in from Asia probably in potting soil and plants imported with ships. It is an all-female species and they reproduce by parthenogenesis (genetic replication of the female snake without the need for fertilisation from a male) meaning a single snake can repopulate an area infinitely.

This is one of the reasons why the relocation of problem snakes should be kept to within 5 – 10 km of where the snake was caught. If you move a snake 50 km (the distance from Pretoria to Johannesburg), you’re potentially moving a snake to a habitat in which they do not naturally occur and probably won’t survive

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For most snakes, there is no threat of them starting a new population and we are not going to see Black Mambas move into Johannesburg or Cape Town. The main reason is that for most snakes you need multiple individuals (at least a male and female or gravid female) to start a viable population, but you also need suitable conditions. It is very important to remember when identifying a snake that distribution maps are one of your best keys - to eliminate species that don’t occur in your area, and to focus on the most likely culprit – BUT keep in mind that - we do occasionally see snakes being unnaturally moved around the country.

Download the free ASI App (ASI Snakes) as it has a feature that lists local snakes throughout South Africa.

The ASI Snakes app has surpassed the 50 000 downloads mark! We're thrilled it has proved to be such a useful app for so many people. We'll be adding some great new features in the upcoming weeks. If you haven't downloaded it yet, you can do so here.http://bit.ly/snakebiteapp.

Our latest video on the Green Mamba is now online! Check it out here.