The bark of trees is an important foraging substrate for a range of vertebrate insectivores. This study aimed to investigate the distribution of food resources available to the bark-foraging insectivore Phascogale tapoatafa, and to compare prey biomass on bark versus the litter layer. We conducted nocturnal sampling for arthropods on tree trunks and litter in a forest in south-western Australia. The bark fauna biomass was dominated by spiders, with cockroaches, beetles and ants also well represented. In contrast, the litter was dominated by orthopterans. Invertebrate biomass was much greater in the litter layer than on tree trunks. Prey items in bark were more plentiful in Melaleuca swamps than in the surrounding dry sclerophyll woodland. Within swamps, trees with the highest invertebrate densities had thin trunks or loose bark, whilst in woodland it was trees with thick bark. Water availability may increase the prey resource used by bark-foraging insectivores.