Alien Terrestrial Invertebrates in South Africa

Abstract

At the time of writing, 466 alien terrestrial invertebrate species have been reported as being established in South Africa. The most diverse groups within this fauna are the insects (330 species; 70.8%), followed by the arachnids (41; 8.8%), annelids (38; 8.2%) and molluscs (33; 7.1%), together accounting for 95.3% of the total. Within the insects, the Hemiptera are the most species-rich group, followed by the Coleoptera. Most of the invasive arachnid species are mites (24 species), many of which are important agricultural pests. The high number of invasive earthworm taxa (38 species) is of concern, given the impacts that alien earthworms have elsewhere in the world. The majority of alien invertebrates were accidentally introduced as contaminants or stowaways, and although exact dates of arrival of most of these remain unknown, many were present over 100 years ago. Also included in the fauna are 95 species of biological control agents that were almost all deliberately introduced and have contributed significantly to the control of 34 invasive plant species (as well as to the control of a few invasive invertebrates). Of the plant species that have been subjected to biological control, 14 are now considered to be under complete control. Most biological control agents are recent introductions and their rates of release are increasing. The most severe economic impacts of accidentally introduced species are as pest species on crops and these can cause considerable losses. These species mostly establish in agricultural habitats dominated by alien plants, or in disturbed and urbanised areas, although some have established in native vegetation. The cryptic nature of many alien invertebrates makes early detection difficult and many probably remained unreported, perhaps decades after their arrival. Regional taxonomic expertise is lacking for many invertebrate groups, so that even native taxa are poorly described. The wider ecological impacts of most alien terrestrial invertebrates remain very poorly known.