20 August 2009

Psacadonotus species - Tettigonioidea

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Psacadonotus sp. - probably P. kenkulun

These katydids are not well known and currently Psacadonotus has only 8 species, of which some are represented from only a handful of individuals and one northern species by a single insect. They mainly inhabit the southern heathland of WA and SA although they are not found on the intervening Nullarbor. In the Esperance district there are three known species, Psacadonotus psithyros recorded west of Ravensthorpe, Psacadonotus serratimerus near Mt Ragged, and Psacadonotus kenkulun that is recorded just a few kilometres away from my sightings and is quite likely the same. The Psacadonotus katydids belong to an interesting group that are flightless and predatory on other invertebrates. The head/body length (excluding the ovipositor) of the illustrated species above was around 5 cm or 2 inches.

Interestingly, most collected Psacadonotus insects are male, whilst all the ones I have encountered were female and of which, two were laying eggs and had their ovipositors deep into the soil, a situation according to David Rentz that is rarely seen. I would imagine the local very deep, fine grained white sands are ideal for their egg-laying activities, I also slash walking tracks and periodically burn pockets of vegetation, both of which provide many small open areas these katydids need and apparently seek. Despite being flightless, these insects do have long legs that are used to walk rather than hop, but they can appear and disappear remarkably quickly, so no doubt could travel a hundred or so metres to reach ideal habitat, likewise the juveniles could disperse the same way, as I have not seen them either.

Being both a grazer and a predator, I would think their most productive food sites would be low-lying areas around receding ephemeral swamps (locally very widespread), where herbaceous vegetation and small invertebrates are more common. So would suspect they spend most of their time around the swamps and flood plains, with the pregnant females visiting the well-drained sandy hillocks to lay their eggs. This could possibly explain my unusual female observations.

The timing of their appearance in this elevated sandy habitat also coincided with rainfall or high humidity and was noted during August, then again at the end of February to the latter part of May. They were not seen in Winter or during the height of Summer.

My thanks to Dr David Rentz for identification.