Te Manahuna Aoraki Project has built what may be the world’s first predator fence to protect an invertebrate
By Devin Murphy on April 21, 2022
The Robust Grasshopper (Brachaspis robustus) is no stranger to leaps of faith. Every jump the chunky grasshopper takes ends in a thud on gravel in dry river beds of Te Manahuna (Mackenzie Basin) on New Zealand’s South Island, but luckily the invertebrates are built to withstand clumsy and rough landings.
“They actually look like a little prehistoric gray tank,” says Simone Smits, manager of the Te Manahuna Aoraki Project in New Zealand. “Most things couldn't throw themselves around like that. They've got an incredible leap on them but while they can jump well they aren’t very good at landing.”
Part of the Robust Grasshopper’s peculiar charm is that it defies most grasshopper characteristics. It doesn’t live in grass, but instead thrives in braided river beds, feasting on lichen growing on the rocks. Its gray color cleverly camouflages it among the gravel, making it difficult to spot unless it flings itself through the air. Female Robust Grasshoppers can grow up to four centimeters long–about the size of your thumb! And the species is very hearty–capable of surviving freezing winter temperatures or blazing hot summers. It is perfectly suited to life in Te Manahuna.
But the grasshopper is classified as Nationally Endangered in New Zealand. There are only a few thousand Robust Grasshoppers in the country, and most of those live in the rivers and terraces of the upper Te Manahuna. New Zealand’s Department of Conservation (DOC) and the Te Manahuna Aoraki Project have been working together to protect the small population of grasshoppers from invasive mammal predators and help their numbers recover.
In 2018, with the support of Re:wild and others, the Te Manahuna Aoraki Project erected a predator fence around a small population of Robust Grasshoppers living on an unused gravel road. The two-mile-road (3.5 kilometers) was built during the construction of the Tekapo Canal during the 1970s. Conservationists are not sure if the Robust Grasshoppers that have made their home on the road moved there naturally, or were accidentally transported there during the canal’s construction, but it has given them the perfect opportunity to study what happens to grasshopper numbers when they are protected from invasive mammal predators.
“We've seen it's a slow population response,” says Smits. “Robust Grasshoppers aren't fast breeders, so it will take a while for us to be able to measure what impact we have had there. While we're waiting for the response in the grasshopper population, what we have seen is even just within a period of six months, is the lizards within the fence increased by five times.”
It isn’t clear yet if the thriving lizards are having an impact on Robust Grasshopper numbers, but DOC has moved them outside the fence as an extra precaution. However, a potentially encouraging sign is that other native invertebrate species within the predator fence, like the Tekapo Wētā, appear to be recovering and rebounding quickly.
“Invertebrates make up 70% of all species on earth. They are part of nature’s food chain and they are integral to the health and function of an ecosystem,” explains Smits.
The Te Manahuna Aoraki Project, along with DOC and students from the University of Canterbury, regularly survey the population of Robust Grasshoppers inside and outside the predator fence. Within the fenced area, they slowly and methodically walk down the road, sweeping their feet back-and-forth in the air before taking each step. That sweeping motion startles the Robust Grasshoppers and allows the team to catch them, tag them and release them unharmed.
After the Te Manahuna Aoraki Project has collected four seasons worth of data on the grasshoppers, they’ll be able to determine if the predator fence is helping the Robust Grasshoppers. The plan is to scale up the project, eventually securing a nearly 1,200-square-mile (310,000 hectares) area in the Mackenzie Basin that is free of invasive mammal predators to protect many native species including the Robust Grasshopper.
“Removing predators from Te Manahuna Aoraki Project area will protect one of the strong holds of the endemic Robust Grasshopper population,” explains Smits.
Devin Murphy is Re:wilds’s senior communications specialist and helps Re:wild and its partners tell stories about the work they do to protect wildlife and wildlands around the planet. Her favorite stories about conservation include fascinating and little-known species and the dedicated humans protecting them.