Unlucky spider flies (Diptera: Acroceridae) trapped in a tomb of mud: An Australian predatory wasp (Sphecidae) provisions its nest with parasitised spiders (Salticidae)

Acroceridae, known as spider flies, are exclusive endoparasitoids of spiders. This study reports the first host association for Ogcodes pygmaeus White, 1914 (Diptera: Acroceridae) after discovering dead acrocerids and their host spiders inside Sceliphron formosum Smith, 1856 (Hymenoptera: Sphecidae) nests in ACT, Australia. From a total of 650 sampled wasp nests, 14 were discovered with multiple spiders parasitised by species of Ogcodes Latreille, 1796. Two species of jumping spiders in the genus Servaea Simon, 1887 (Araneae: Salticidae), including an undescribed species, were identified as hosts of O. pygmaeus in this study. We hypothesise that the parasitised spiders were brought back to the nest as S. formosum prey items, and when acrocerid adults emerged they were trapped inside the sealed nests. Dead pupae were also found in the nests along with the dead adult acrocerids. To our knowledge, this entrapment of spider parasites inside S. formosum nests has not been documented before, and this study represents a new method for obtaining acrocerid fly host records.