by Helen Jones
In February 2006 I spent two weeks travelling in Kakadu National Park in the company of a small 'Go Bush' group.
One of the objects of the trip was to find populations of the brightly coloured but elusive grasshopper Petasida ephippigera that was observed by Ludwig Leichhardt on his 1844-5 expedition from Moreton Bay to Port Essington. We located the preferred food plant of this grasshopper at various times but no grasshopper. We were mostly looking just before a rain shower and perhaps they hide when it rains.
A late afternoon trip to a swimming hole near the upper edge of the escarpment took us into some quite thick scrub and there they were – Leichhardt's Grasshoppers – just as Leichhardt had described them. They are endemic to the sandstone escarpment as are the Pityrodia shrubs (Pityrodia jamesii) on which they were feeding when we found them.
In the dry weather the eggs of Leichhardt's Grasshopper hatch after being dormant during the wet season. The young nymphs climb onto their host plant, the aromatic Pityrodia Bush, and by the time the next wet season arrives they have progressed through their various growth stages then moult into their adult colours of brick red, blue and black. Then the adults begin mating and the process starts again.
It is thought that these brightly coloured insects, which are so obvious from a distance, are toxic to would be predators as they do not seem to have any enemies. They occur in low numbers and form sporadic colonies throughout the stone country. It is believed fire may be the major factor in limiting their occurrence.
When home I did a bit of research into when and where Leichhardt came across these grasshoppers. I tracked down a copy of 'Ludwig Leichhardt Journal of an Overland Expedition in Australia from Moreton Bay to Port Essington 1844-45' on the Internet. I also found a paragraph in 'Grasshopper Country' by David Rentz suggesting that a paper by Calaby and Key would give some interesting history of its early discovery, 70 year absence, subsequent rediscovery and identification of its host plant.
I spent ages reading Leichhardt's Journal. Eventually I came across one sentence, dated November 17, 1845 –
'Whilst on this expedition, we observed a great number of grasshoppers of a bright brick colour dotted with blue: the posterior part of the corselet and the wings were blue; it was two inches long, and its antennae three quarters of an inch.'
Next I acquired a copy of the paper written by Calaby and Key titled 'Rediscovery of the Spectacular Grasshopper Petasida ephippigera' in the Journal of the Australian Entomological Society in 1973. According to this paper, the first specimen was collected by the purser of the H.M.S. Beagle during a 1837-1843 survey expedition which travelled 260 kms along the Victoria River, Northern Territory.
The second specimen was recorded in 1845 when Leichhardt's expedition was on the escarpment above the South Alligator River N.T. looking for a way down into the forest and grassland. A third was recorded in 1855-6 and another was mentioned in 1904 as being in the Museum d'Histoire Naturelle in Geneva. Then there was a gap of about 70 years until J.H.Calaby found a single grasshopper in the general vicinity of the South Alligator River N.T.
This discovery was followed by many others and the next puzzle was to find the food plant which was eventually narrowed down to the shrubs Pityrodia and Dampiera. As noted before Pityrodia is endemic to Arnhem Land; Dampiera is not but is found in Keep River National Park as is Leichhardt's Grasshopper.
- Ludwig Leichhardt Journal of an Overland Expedition in Australia from Moreton Bay to Port Essington 1844–45
- Stanley Breedon and Belinda Wright – Looking after the Country the Gagudju Way 2001.
- Calaby and Key 1973 'Rediscovery of the Spectacular Grasshopper Petasida ephippigera WHITE'. Journal of the Australian Entomological Society 12. 161-164.
Rentz David Grasshopper Country CSIRO/UNSW Press
Brock John Native Plants of Northern Australia 1988
Morris Ian Kakadu National Park Australia 1996.
Page URL: https://www.disjunctnaturalists.com/articles1/leichhards-grasshopper.htm