Gaudy grasshopper brings on the wet
In Australia's Top End a beguiling grasshopper is heralding the coming of the wet season by putting on its gaudiest outfit. Leichhardt's Grasshopper is out in full adult glory. It's Australia's most brightly coloured grasshopper and one of the most spectacular in the world.
Leichhardt's Grasshopper is bright red, blue and orange. Its strong colours are a defence against predators which works so well that this little grasshopper has Attitude - often it doesn't even bother to fly away when predators approach.
It's named after the explorer, Ludwig Leichhardt, who reported great numbers of them as he crossed the Arnhem Land plateau in 1845. However, after a few more sightings, Leichhardt's Grasshopper went incognito for 120 years. It's only reappeared on the scientific record recently, around 1973, when the mining industry boomed and access into Leichhardt's grasshopper territory was improved.
The Jawoyn and Gundjeibmi people of Western Arnhem Land call the grasshopper Alyurr, children of the lightning man, Namarrgon, a powerful ancestral being.
The country around Darwin and across to Arnhem Land has one of the highest incidences of lightning in the world. Namarrgon is commonly depicted in the regions rock art with axes hanging from his body, which he uses to strike the clouds. Around Kakadu the axes on his head represent grasshopper's antennae.
The peak time for lightning is November–December during the 'build-up' when spectacular dry thunderstorms light up the skies.
At this time of year, Leichhardt's grasshopper is said to be out and about looking for the lightning in its new gaudy outfit.
Where: The country around Darwin and across to Arnhem Land
The seven 'looks' of Leichhardt's Grasshopper
By the time Leichhardt's Grasshopper emerges in full adult glory it has already had seven style changes.
It begins as a nymph, hatching from eggs in the early stages of the dry season (around April). The nymphs already look like grasshoppers but they are tiny, only half a centimetre in length. They are well camouflaged, and their wings are like little stumps.
The young grasshoppers grow very slowly until about August when the temperature and humidity increase rapidly, then both host plants and grasshoppers speed up in growth. They go through seven instars or growth stages, shedding their skins after each stage.
In September–October they begin to get more colour and around November they emerge in full adult splendour.
It takes another two to three weeks for them them to become reproductively mature. Mating takes a few more weeks and sometime in January and February the females begin laying their eggs in wet sand. Their bodily systems then slow down and the grasshoppers literally fall off the twig and can be found dead around the base of their host plant.
When young Leichhardt's Grasshoppers reach about 3.5&38211;4 centimetres about one or two stages from adulthood. they tend to aggregate slightly to about two or three grasshoppers per bush.
The boys are easy to tell from the girls. Male aduts are smaller and more slender. The females get quite fat and chunky from all the eggs they're carrying in their abdomen. Males will often spend a long time perched on top of the female keeping other males away from her before actually mating.
Where can I see it?
The grasshopper lives in what local people call the "Stone Country", especially on the huge sandstone plateau of Arnhem Land rising 300 metres out of the surrounding plains. It's been found only in the Northern Territory and occurs in small, isolated populations in three main locations.
Kakadu National Park has a number of sites including some near Nourlangie Rock about 40 kilometres south of Jabiru. There are populations in Nitmiluk National Park near Katherine and the Keep River National Park on the border with Western Australia. It's also occasionally sighted on cattle stations near the parks.
Catching sight of these grasshoppers requires a bit of effort and some patience. Most sites are accessible only by foot more than a day's walk from any roads. Even then it may not be worth it. Numbers fluctuate so greatly that grasshoppers may only be around one year in three.
This remoteness has made Leichhardt's Grasshopper difficult to study and also to protect. Even though it is quite rare, the grasshopper isn't able to be covered by Endangered Species Legislation because we don't fully understand its basic distribution, biology and ecology.
Lyn Lowe is a research scientist with CSIRO Tropical Ecosystems Research Centre. In 1992 she monitored 5 populations of Leichhardt's Grasshopper in Kakadu National Park for 18 months. Since January 2000 she's been working on the life history of Leichhardt's Grasshopper. Every six weeks she travels to Mt Borradaile, in Western Arnhemland to monitor several populations of Leichhardt's Grasshoppers.
In 1991 Leichhardt's Grasshopper featured on an Australian 80-cent stamp and it's beginning to feature prominently in Northern Territory tourist publications.
True to its tree
Leichhardt's grasshopper likes to stick to the same kind of food, a resinous bush that's common in sandstone country. At Keep River it eats Pityrodia ternfolia, at Nitmiluk near Katherine it eats Pityrodia pungens and at Kakadu National Park and Mt Borradaile it eats Pityrodia jamessii.
Leichhardt's Grasshopper not only sticks to one type of plant species, it also often sticks to one actual bush. When first hatched they live around the base of their host plant, a very aromatic plant called pityrodia. Over their life cycle they gradually move higher up the plant. It's thought that only the adults can tolerate high concentrations of the strong compounds in the pityrodia. Generally the leaves at the bottom of the plant have lower concentrations of the chemical compounds, while the new growth further up has higher concentrations.
The best hosts are bitter
Brightly coloured insects are often chemically defended against vertebrate predators. They usually do this by having internal toxins or by secreting or regurgitating toxic substances. Chemists Mary Fletcher and William Kitching from the University of Queensland recently analysed several pityrodia species and found the plants contain turpene compounds associated with glycoside sugar groups which are likely to be bitter tasting.
It's still to be determined whether the adult grasshoppers store these compounds in their body to form a chemical defence.
Many plants but few grasshoppers
One of the conundrums about Leichhardt's Grasshopper is that although it only occurs in small populations that are totally dependent on one food source, the food source is actually quite widespread.
One possible reason for the grasshopper's low numbers is other invertebrates.
In the dry season many spiders, wasps and other insects also congregate on the pityrodia plants. And while the grasshopper's bright colours, especially the orange are a good deterrent against vertebrate predators like birds, it can't depend on these against the invertebrates.
Another reason for the grasshoppers low numbers is that Leichhardt's Grasshopper might be getting burned to death.
Much of the controlled burning in the Northern Territory's National Parks happens in May and June. This is precisely the wrong time to to burn for Leichhardt's Grasshopper according to Lyn Lowe. At this time, the juvenile grasshoppers don't have wings, so they can't easily escape the fires. Their host plant Pityrodia is fire tolerant and grows back lush and green. But even if the young grasshoppers do survive by falling into cracks or under rocks, the food source takes 3 to 4 weeks to recover. Meanwhile, the grasshoppers die of starvation.
Lyn Lowe suggests late November and early December for burning Leichhardt's Grasshopper terrritory. There's more humidity in the air and more moisture in the grass, which together tend to make for a cooler burn. Also the fire usually doesn't spread as far and sometimes goes out overnight. All this, plus the fact that the grasshopper can now fly, means it will have more of a chance to get away.
With limited park resources, custom designed fire regimes are not easy to conduct but they may be vital for Leichhardt's Grasshopper's continued survival.
Of the five grasshopper sites in Kakadu National Park that Lyn began studying in 1992, four were burnt out within 2 years and Leichhardt's Grasshopper could no longer be found there. Eight years later they still haven't come back. Only one of the sites still has Leichhardt's Grasshopper occurring on it and it's the only site which is well protected from most fires. Lyn's new study site at Mt Borradaile in western Arnhem Land is actively protected against fire.
Australia: grasshopper country
Leichhardt's Grasshopper's scientific name is Petasida ephippigera. Grasshoppers come from the group of insects known as Orthoptera, which includes crickets, locusts and grasshoppers.
Grasshoppers are particularly successful in Australia. Across the continent are 2000 species with a very high number, about 93–100 per cent endemic (found only in Australia).
Leichhardt's Grasshopper is one of the short-horned grasshoppers (Califera), one of the thousand species in Australia. They have strong and robust antenna compared with long horned grasshoppers such as katydids and crickets, and tend to have better eyesight than their long horned cousins.
Leichhardt's Grasshopper belongs to the subgroup Pyrgomorphidae which are often strong coloured and often have a single host. Several African species exude liquids or frothy material from their body such as their leg joints, to put off predators. Some of them are poisonous. Leichhardt's Grasshopper occasionally regurgitates a sticky brown liquid when it's disturbed but it's not yet known whether this is toxic.
Strangely the Leichhardt grasshopper's closest relative is far off in the south-west of Western Australia. It too has a single host plant.
- Penny Greenslade and Lyn Lowe. Leichhardt's Grasshopper, Nature Australia, Autumn 1998
- J.H. Calaby and K.H. L. Key. Rediscovery of the spectacular Australian Grasshopper Petasida ephippigera White (Orthoptera: Pyrgomorphidae) Journal of the Australian Entomological Society, Volume 12, pp161-164, September 15, 1973.
- Lyn Lowe. Preliminary investigations of the Biology and management of Leichhardt's grasshopper, Petasida ephippigera White. Journal of Orthoptera Research No. 4, August 1995
- Mary T. Fletcher(1), Lynette Lowe (2) and William Kitching(1). Chemistry of Leichhardt's Grasshopper", 10th Brisbane Organic Chemistry Symposium, 29th November 1996 (1) Department of Chemistry, University of Queensland, 4072 (2) CSIRO Division of Wildlife and Ecology, PMB 44 Winnellie NT 0821
- David Rentz. Grasshopper Country: the abundant orthopteroid insects of Australia. UNSW Press 1996.
- George Chaloupka. Journey in Time: the world's longest continuing art tradition. The 50,000 year story of the Australian Aboriginal Rock Art of Arnhem Land. Reed Books 1993
- Paul Tacon: From Rainbow Snakes to 'X-Ray' Fish: the nature of the recent rock painting tradition of Western Arnhem Land, Australia. PhD Thesis. Prehistory and Anthropology, Faculty of Arts, Australian National University.
- Allan Lees. "Singing in the Rain: a visit to Kakadu National Park's Nourlangie Rock when it is really pouring". Geo Volume 8 No.4
Published 02 November 2000