There is a paucity of studies examining direct impacts of introduced alien species on biodiversity, a key need for motivating for alien species control in conservation areas. The introduced prickly pear (Opuntia stricta) has invaded some 35 000 ha of Kruger National Park. We investigated the effect of O. stricta on beetle and spider species assemblages in the Skukuza region of Kruger National Park. We used unbaited pitfall traps over a 12-month period in four treatments of varying O. stricta density. Species richness, species density and abundance of beetles and spiders were compared. A total of 72 beetle and 128 spider species were collected. Species richness and species density for beetles and spiders did not differ significantly across the four treatments. Assemblages for spiders did not differ across treatments but beetle assemblages were significantly different from uninvaded control sites. This study suggests that the current density of O. stricta does not significantly affect spider species richness, density or assemblages but that beetle assemblages are significantly affected.