This study determines the impact of an invasive herbaceous weed Tradescantia fluminensis on invertebrates within three lowland podocarp/ broadleaved forest remnants in southern North Island, New Zealand. Epigaeic invertebrates were sampled within three Tradescantia-infested plots and three non-infested plots at each of three sites using pitfall traps. The abundance of invertebrates was reduced in Tradescantia plots compared with non-Tradescantia plots if Collembola and Acarina, the two most abundant and variable orders, are excluded (647 +/- 123 (mean SE) compared with 1153 +/- 370), though this difference is not statistically significant. There was no difference if they were included (3897 +/- 2530 compared with 2505 +/- 1095). Five of the 23 orders collected were sorted into recognisable taxonomic units (RTUs). RTU richness was lower in Tradescantia plots compared with non-Tradescantia plots (39.7 +/- 5.5 compared with 51.7 +/- 8.9) though there was weak statistical support. Deirended correspondence analyses separated Tradescantia and non-Tradescantia plots within sites when based on RTUs, but not when based on orders/families. Overall, impacts of Tradescantia were apparent despite large differences in invertebrate assemblages among sites. The impact of Tradescantia could be a result of the weed's tall, dense vegetation structure and associated microclimate, relative to native ground covers. (C) 2003 Elsevier Ltd. All rights reserved.