Philosophiae Doctor - PhD / The order Orthoptera contains a wide diversity of species and is the most speciose of the polyneopteran insect lineages. In South Africa, the orthopteran fauna is abundant and diverse, with approximately 88% of all Southern African species occurring in the region. One highly endemic and conservationally important group, the Pneumoridae (commonly known as bladder grasshoppers), is recognized as being an evolutionary distinct lineage, with all species occurring either fully or partially within South Africa. Unfortunately, the understanding of the true extent of diversity for this paleo-relictual group is hampered by inaccuracies in current taxonomic descriptions and the lack of adequate survey data. The last taxonomic revision was undertaken >50 years ago, during which several taxonomic discrepancies and uncertainties were introduced, particularly within the genus Bullacris. Specimens may be difficult to classify due to significant morphological overlap between species, geographic variation within species, and confusion arising from alternative male morphs being designated as separate species rather than conspecific within existing species. Furthermore, paleo-relictual insects are of great evolutionary and biogeographical interest by virtue of being survivors of highly derived lineages, which allows for insights into the paleo-history and phylogenetic diversity of a region. Thus, the aims of this research were, firstly, to investigate the biogeographic patterns of diversity for South African Orthoptera and to place the Pneumoridae family into this context, secondly, to construct a molecular phylogeny for the Pneumoridae and estimate divergence times by genetically analysing the relationships between Pneumoridae species, and lastly, to update taxonomic descriptions in the genus Bullacris. Biogeographic analyses were performed by making use of a national orthopteran database created from historical and current collecting records, and performing hierarchical cluster analyses to delimit zoogeographic regions and centres. A dated phylogeny was created by extracting DNA from fresh and museum specimens, and generating Bayesian Inference, Maximum Likelihood and BEAST phylogenetic trees for the Pneumoridae family. The updated revision of the genus Bullacris included morphological, acoustic and genetic comparisons. Results from the biogeographic analyses showed that there was a clear east (summer-rainfall) and west (winter-rainfall) primary biogeographic division for orthopteran species, which has also been previously noted for other insect taxa. Six zoogeographic centres were retrieved: the Central Nama-Karoo, the Cape Fynbos and the Succulent Karoo centre located in the west and the Savanna, the South-East Tropical and the Indeterminate Summer-Rainfall centre located in the east. Orthopteran species richness was found to be evenly distributed throughout the bladder grasshoppers diverged from other orthopteran species during the early Cretaceous period, at an estimated 134.70 MYA. The first group to have diverged within the pneumorid family were the Forest species at approximately 116.91 MYA, followed by the Fynbos, the Succulent Karoo and then the Savanna species groups. It is suggested that bladder grasshoppers originated in South Africa and dispersed northward due to climatic changes. In addition, the phylogeny of the family showed that the species Physemacris variolosa integrated with members from the Bullacris genus. Lastly, the taxonomic revision of the Bullacris genus indicated that B. discolor and B. serrata were acoustically and morphologically similar, and had relatively low mitochondrial pairwise variation, and could thus possibly be represent sub-species. In addition, B. membracioides and B. intermedia were acoustically similar and also had low mitochondrial pairwise distances; however, statistical analyses showed significant morphological differences. Therefore, there was insufficient combined evidence to amalgamate species. Nevertheless, there are several environmental factors that could explain these variations, and it is therefore suggested that additional data is required to solve these taxonomic discrepancies. The results derived from this research have provided interesting insights into the evolutionary history of the Pneumoridae, the environments in which they occur, and share with other orthopteran species. Together with the newly discovered phylogenetic relationships and biogeographic studies, this information is useful data for conservation management strategies and expands our knowledge on the evolutionary histories of South Africa’s entomofauna.country; however, the Cape Fynbos centre has representatives for most orthopteran families. The dated phylogenetic analyses revealed that