none no species Nest structure, nesting behaviour, nesting success and nest mortality factors of eleven species of aculeate wasps were compared. Seven species nest in pre-existing cavities: Auplopus femoralis (Arnold) and A. vitripennis Smith (Pompilidae), Chalybion laevigatum (Kohl), Isodontia pelopoeiformis (Dahlbom) and I. stanleyi (Kohl) (Sphecidae), Tricarinodynerus guerinii (Saussure) and Proepipona meadewaldoi Bequaert (Eumenidae). These were studied using trap-nests. Four species construct aerial mud-nests: Afreumenes aethiopicus (Saussure), Delta hottentottum concinnum (Saussure) and Synagris analis Saussure (Eumenidae) and Sceliphron spirifex (L.) (Sphecidae). Study sites were in Natal and the Eastern Cape in South Africa. Overall nesting success, as measured by the proportions of successful cells, differed in only one of the species. In some cases interspecific success rates differed significantly but inconsistently between localities, due mostly to varying levels of nest parasitism and other mortality factors. The most important identifiable causes of nest/cell failure were attacks by Miltogramminae (Diptera), Chrysididae and Eulophidae (Melittobia sp.) (Hymenoptera) with the addition of Osprynchotus sp. (Hymenoptera: Ichneumonidae) in aerial mud-nests. Ceropales punctulatus Cameron (Pompilidae) and Leucospidae were very host specific and therefore not of general importance. A number of other taxa including Stenarella sp. (Hymenoptera: Ichneumonidae), Mutillidae (Hymenoptera) and Bombyliidae (Diptera) caused mostly low mortality. Endogenous mortality, caused by a combination of unidentifiable factors, was also important. Chalybion laevigatum and T. guerinii were particularly susceptible to parasitism by Miltogramminae and Chrysididae respectively. Possible effects of nesting characteristics on nest parasitism are considered in the light of the evidence obtained. Certain characteristics of aerial mud-nests and their influence on parasitism are discussed with reference to nests of S. spirifex. It was concluded that nesting success depended largely on the activities of parasites. The unique nesting habits of each aculeate species provided protection only against specific types of parasites and success was therefore affected by the interaction between nesting habits and the size and species composition of parasite populations. Reproduction; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Ecology; Population dynamics; Animal constructions; Land and freshwater zones; Ethiopian region Miltogramminae (Sarcophagidae ); Bombyliidae; Hymenopteran hosts; Aculeata; Nest mortality; South Africa; Cape Province & Natal, host mortality Hymenoptera; Hymenopteran hosts; Aculeata; Nest mortality; South Africa Aculeata; Reproductive productivity; Nesting success; Dipteran parasites; Bombyliidae & Miltogramminae; Hymenopteran parasites; Host nest mortality; Mortality; Nests; Structure; South Africa; Cape Province & Natal; Nest structure & nest mortality, dipteran & hymenopteran parasites