You won’t find the bedraggled Joburg “prawns” of Oscar-nominated science fiction thriller District 9 in the new book by UCT zoologists Charles Griffiths and Mike Picker, but these authors account for pretty well every other alien and invasive animal that occurs in South Africa.

In fact, the associate professors and their specialist co-writers believe their book, Alien and Invasive Animals – a South African perspective, represents the most comprehensive current listing of these animals to date.

They put the total number of introduced animals in South Africa at 601 – 487 terrestrial species, 38 freshwater and 76 marine – although they say this is “certainly” an under-estimate, partly because many potential introduction sites and animal groups have not been sampled and partly because of a lack of taxonomic knowledge of many invertebrate groups.

“That number, which excludes animals in captivity, is a real surprise to people – it’s a lot,” says Griffiths.

And, probably surprisingly, you’ll find a fair number of them in your back garden, including earthworms, of which there are between 40 and 50 species and which were rare historically in Cape Town because of an absence of leaf litter in fynbos areas.

It also includes almost all the snails and woodlice – in fact, almost all the forest fauna found in suburban gardens are introduced.

Griffiths, who is passionate about photography, particularly macro-photography, provided many of the illustrations in the book.

“It’s quite remarkable how many I was able to take in my own garden in Claremont – snails, slugs, woodlice, aphids, cockroaches, centipedes and the millipedes and so on,” he says.

A marine specialist who recently described his 100th new species, and who has also described the first recorded presence in South Africa of “at least another 100”, Griffiths believes their book is unique.

He says the alien and invasive plant species in South Africa – more than 8 750, of which 161 now rank as serious pests causing economic and ecological damage estimated at more than R100 billion each year – have been well documented, and that there are also books that include some groups of alien and invasive animals, such as birds or marine invasives. “But there’s nothing that looks at all the habitats and the taxonomic groups together.”

While the authors list 601 alien and invasive animal species, they describe and illustrate more than 300 in the book. These are divided into 33 groups – such as mammals, birds, fishes, beetles, butterflies and moths, cockroaches, termites, sponges – with each chapter written by either Griffiths or invertebrate specialist Picker or by (or in conjunction with) one of 19 other specialists who are among South Africa’s top biologists.

“We tried to pull in the best brains in the country... the best in their fields,” says Griffiths.

For example, he co-wrote the chapter on segmented worms with Danuta Plisko, an 82-year-old Natal Museum researcher who is still extremely active. “She told her colleagues: ‘I don’t have time to die’.”

Some alien and invasive species are a problem everywhere in the world and there is an immense number of them, many “quite definitely severely damaging”, Griffiths explains.

“So although our book is a South African perspective, part of it is very global. For example, mice, rats, cockroaches and many agricultural pests such as snails have spread just about everywhere that humans have gone. They are all purely negative and have no beneficial uses at all.”

Some of these species, like their plant equivalents, cause significant economic costs, with the agricultural pests being the most obvious. They include the mite that is affecting the vigour of honey bee colonies around the world and causing losses estimated at billions of dollars, mostly in lost fruit production because of a lack of bees to pollinate the trees.

There are also many species that are “fairly benign” but not necessarily beneficial, such as millipedes, the European starling and the grey squirrel from America, Griffiths points out.

Then there are those that are beneficial, notably the many bio-control agents like the acacia gall wasps that have been deliberately introduced to control other alien invasive species.

Another arguably benign and beneficial alien is the European mussel, although this “depends on who you are”, he says. For the African black oystercatcher, the presence of this mussel increases the amount of food available “tremendously”.

“This is because these mussels occur higher on the shore than indigenous mussels and there are many more of them, so this means the birds have more hours in which to feed,” Griffiths explains.

But these mussels have also at least partly displaced some indigenous marine species, and there’s no clear-cut answer as to whether their presence is, in overall terms, beneficial.

Some alien species were thought to be entirely beneficial when they were introduced, but have proved to be highly damaging. Bass and trout species introduced into local streams and rivers for sport fishing are a case in point, Griffiths suggests.

“It’s only been 100 years later that we’ve really understood that these fish radically change the food chain and are competing with, and often eliminating, rare indigenous fish.”

He and Picker believe the correct response is to accept there are large parts of South Africa that have been permanently transformed by alien and invasive species, and that attempts to remove them will be pointless.

“But we must also be very careful to ensure that we keep at least some areas completely free of alien species, where the indigenous species can survive and where we can see and understand what these areas were like historically.” - Cape Argus

l Alien and Invasive Animals – a South African perspective is published by Struik Nature, ISBN 978 1 77007 823 9

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