Imagine a creature that turns moths into mummies by trapping them in an underground grave before emerging out of their neck to begin the cycle again. Not only does this creature exist, it’s part of New Zealand’s native biota and although referred to as the vegetable caterpillar, we are actually talking about a type of fungus – Ophiocordyceps robertsii.
Further research and scientific advances can reveal additional information that result in taxonomy changes. DNA testing of Cordyceps robertsii and related fungi has seen a name change to Ophiocordyceps robertsii.
How does this happen?
The caterpillars of the native Aoraia dinodes or Dumbletonius characterifer species of moths accidentally eat the very small, reproductive spores of the fungus when feeding on leaf litter. The insides of the caterpillar form an ideal habitat for the fungus spores to germinate and grow. When the caterpillar retreats underground to start to form into a pupa, preparing to develop into a moth, the fungus starts to grow using the caterpillar’s body for food. As the fungus grows, it forms a shell around the caterpillar’s body, and slowly the whole thing dries out. The caterpillar is slowly turned into a mummy and is dried and preserved in the fungal casing.
As the fungus feeds from the nutrients in the caterpillar’s body, it grows and is eventually ready to reproduce again. It grows a small stem through the head of the caterpillar, which is the part of the body closest to the forest floor. The stem grows slowly until it pushes through to the forest floor. When it reaches the fresh air, the top of the stem thickens to develop a layer of flask-shaped structures in which are produced fungal spores in sets of eight, each set within a sac called an ascus. These are released into the atmosphere, to be inadvertently consumed by another unsuspecting caterpillar moth, and the cycle begins again.
Signs of the vegetable caterpillar can be found in New Zealand bush. Look for small (2–3 millimetres thick) brown stems pushing up through the leaf litter. If you carefully dig these out, you might see the moth mummy that is often still attached at the bottom, dried and preserved by the fungus.
Is the fungus useful?
Recent research in New Zealand has been focusing on the traditional uses of fungi like the vegetable caterpillar fungus. Dr Peter Buchanan and his master’s student Rebekah Fuller have been investigating the uses Māori had for native fungi species. Rebekah has been working with Māori communities throughout New Zealand and has interviewed them about their knowledge of fungi. Their results are interesting.
Traditionally, Māori looked for the vegetable caterpillar fungus and sometimes used it for food. Apparently, when fresh, it tastes a little like a nut. The more common use was as an ingredient of the ink used to create tā moko (tattoo). Learn more about using āwheto for tā moko in Māori knowledge and uses for fungi.
Nature of science
One characteristic of good science is when scientists listen to contributions from everybody when they are developing understandings of phenomena. The vegetable caterpillar shows us how Māori knowledge has opened up interesting avenues for research.
Selling mummified caterpillars
At the beginning of the 1900s, the Auckland to Rotorua train would slow considerably on an incline through what was the primeval Mamaku Forest. People were able to run alongside the train and sell the mummified caterpillars to tourists as curios. The caterpillar mummies sold for the fortune of 10 shillings each.
Further research and developments
Development of the āwheto fruitbody is a natural process of interaction between fungus and caterpillar. Research seeking to artificially cultivate fruitbody development has been unsuccessful. Overseas, considerable effort has been applied, also without success, to artificially cultivate a high value āwheto-like fungus that inhabits the alpine grasslands of Himalayas and Tibet. Ophiocordyceps sinensis produces its fruitbodies on caterpillars of the ghost moth, and is harvested by local communities in vast, unsustainable quantities (est. 82 tons per year) for the Chinese herbal medicine market. With declining harvests likely resulting from over-exploitation, this has become one of the world’s highest-priced natural biological products, with an average retail price of US $45,000 to 90,000 per kg. Its value and reputation as an aphrodisiac and tonic has attracted interest in other species of Ophiocordyceps such as the vegetable caterpillar fungus. But to date research is suggesting it appears to lack key bioactive chemicals and is distinctly larger in appearance.
This cross-curricular activity combines science with reading, viewing, writing and presenting and will help your student learn about two unusual native New Zealand soil creatures, one of which is the vegetable catapillar.
Listen to the Department of Conservation's Threatened Species Ambassador, Nicola Toki talk about this wonderous critter on Radio NZ here.