Patterns in pitfall captures of millipedes (Diplopoda: Polydesmida: Paradoxosomatidae) at coastal heathland sites in Tasmania

The millipede by-catch from a 1986-88 spider survey in Tasmanian coastal heathland was tallied by species, sex and life-stage. Two species of paradoxosomatid Polydesmida, Notodesmus scotius Chamberlin, 1920 and Pogonosternum sp., made up 99.8% of the pitfall captures. The N. scotius catch (9754 individuals) was 80% adult (stadium VIII) and peaked in October-December with only 23 captures in July-September. The Pogonosternum sp. catch (116 individuals) was 91% adult and peaked in September, with 40% of all captures in July-September. These results, together with field observations, indicate that pitfall trapping mainly captured adults wandering during the mating season, and that mating seasons for the two species did not coincide. The Pogonosternum sp. captures were tightly clustered in space, showing that pitfall trapping can be an unreliable method for estimating millipede abundance unless the fine-scale spatial patterning of target species is known in advance. A third paradoxosomatid species known to be present near the survey sites, Dicranogonus sp., did not appear in any of the 938 pitfall samples containing millipedes. The overwhelming dominance of paradoxosomatid Polydesmida in heathland is in marked contrast to the dominance of dalodesmid Polydesmida in forest habitats in Tasmania.