The life histories, densities and distribution patterns of the most abundant macroinvertebrates, exclusive of chironomids and oligochaetes, are reported for a low-gradient, second-order, blackwater stream on the Coastal Plain of South Carolina, USA. Univoltine life histories were found for all species of Coleoptera (Ancyronyx variegata, Macronychus glabratus, Dubiraphia quadrinotata and ... [Show full abstract] Hydroporus clypealis) and most species of Ephemeroptera (Eurylophella temporalis, Paraleptophlebia volitans and Hexagenia munda), although the mayfly Stenonema modestum was at least bivoltine. Both univoltinism (Macrostemum carolina and Pycnopsyche luculenta), partial bivoltinism (Nyctiophylax affinis) and complete bivoltinism (Hydropsyche decalda, Cheumatopsyche sp., Phylocentropus placidus and probably Chimarra florida) were found among the Trichoptera. Odonate species were both univoltine (Calopteryx dimidiata, Enallagma divagans and Epitheca cynosura) and semivoltine (Boyeria vinosa, Gomphus lividus and Macromia georgina). The alderfly Sialis aequalis and the isopod Asellus laticaudatus were univoltine, while the blackfly Simulium taxodium produced at least 6 generations per year. Groups of functionally-related species within the orders Odonata, Trichoptera and Coleoptera each exhibited possible temporal and/or spatial segregation.