Carabidae in a coal mine?: Forensic analysis of Hawai‵i’ insect apocalypse

Revisionary systematics supported by robust biotic survey prospectively elucidates biodiversity. When done along with comprehensive examination of historical specimens, putative extirpation of taxa can be assessed. Taxonomic revision of native Hawaiian carabid beetles has been completed with recently described taxa doubling the recorded fauna to over 400 species. Early British collectors in Hawaii recorded the habitats of their subjects, allowing species loss to be viewed through the lens of natural history. Using Oahu as an example, ecological factors associated with carabid species loss include numerical rarity coupled with geographically restricted distributions, occurrence within ground-level microhabitats and occupation of sites from 400–900 m elevation. Such parameters put individuals of lost species in direct contact with alien, invasive ants, within habitats modified by feral ungulates and invasive plants. In one spectacularly counterintuitive instance, Blackburnia tantalus (Blackburn), the most commonly collected carabid beetle in Oahu during the early historical period, was last observed in nature in 1940. These flight-capable beetles were distributed throughout Oahu where they occupied numerous microhabitats. However, they formed large ground-level over-wintering aggregations, and  93% of specimens were collected at sites below 700 m elevation, well within the elevational range of  big-headed ant, Pheidole megacephala F., an alien invasive established prior to 1877. R.C.L. Perkins observed Pheidole workers preying in large numbers upon native Hawaiian beetles, suggesting such predation contributed to extirpation of B. tantalus. Though its extinction could never be observed directly, numerical dominance and broad geographical distribution did not guarantee continued existence of this previously abundant species.