7.2 Composition of the Known Alien Terrestrial
Invertebrate Fauna
The current composition of the established alien terrestrial invertebrate fauna,
including 35 species that have been added since 2011 and that are highlighted in
Table 7.1, is estimated to comprise 466 species. All but three of the species added
since 2011 are insects, and 16 of these are deliberately released as biological control
agents on insects. Unsurprisingly, given the overall diversity of this group, by far the
largest component of the fauna comprises insects (330 species or 70.8%), followed
by arachnids (41 or 8.8%), then annelids (38 or 8.2%) and molluscs (33 or 7.1%).
These four major groups thus together make up 94.9% of all established alien
terrestrial invertebrates. The number of biological control agents totals 95 species.
Biological control is discussed in more detail by Hill et al. (2020, Chap. 19; see also
Hajek et al. 2016; Kumschick et al. 2016), thus only a brief synoptic account is
included here (Fig. 7.1).
Table 7.1 Updated count of alien terrestrial vertebrates known in 2018, showing current number of
species per group, the increase in number since 2011 and the number of biological control agents in
each group
Group name
Number of species
Species added
since 2011
Number of biological
control species
Collembola
13
0
0
Zygentoma
3
0
0
Blattodea
5
0
0
Dermaptera
5
1
0
Phasmatodea
1
0
0
Embioptera
1
0
0
Psocoptera
1
0
0
Hemiptera
104
8
16
Thysanoptera
5
2
1
Phthiraptera
13
0
0
Coleoptera
87
6
45
Lepidoptera
25
3
8
Diptera
32
4
9
Siphonaptera
5
0
0
Hymenoptera
30
7
15
Myriapoda
9
0
0
Arachnida
41
2
1
Crustacea
8
1
0
Nematoda
5
0
0
Annelida
38
0
0
Mollusca
33
1
0
Platyhelminthes
2
0
0
Total
466
35
95
Note: Aquatic species listed by Picker and Griffiths (2011, 2017) are excluded
7 Alien Terrestrial Invertebrates in South Africa
187