Once believed to be secure because it was assumed to live above the level of rat invasion, Deinacrida pluvialis shows declines of more than 90% over 30 years at two localities in the Southern Alps
Southern Alps giant wētā Deinacrida pluvialis nymph. Westland. Photo © Danilo Hegg
When two populations of the Southern Alps giant wētā Deinacrida pluvialis were first discovered in 1992, surveys led by George Gibbs found 43 wētā in three person-hours spent turning rocks in the Matukituki River West Branch (Mt Aspiring National Park), and 36 wētā in 13 person-hours searching in Price Basin (Whitcombe River, Westland). At the time, the wētā was assumed to be inaccessible rather than rare, and was considered safe under the assumption that it lived above the level of rat invasion (Gibbs 1998). The species was listed “Not Threatened” in the New Zealand Threat Classification System (NZTCS); no more surveys were conducted in almost 30 years. It was only around 2015 that scientists started raising the alarm. By the time we surveyed the West Matukituki head cirque again in 2021, we could do nothing but document the extinction of the local wētā population. The following year, the species was thus reclassified “Threatened, Nationally Endangered” (Trewick et al. 2022).
In a paper recently published in the New Zealand Journal of Zoology, Wētā Conservation Charitable Trust (WCCT) chair Danilo Hegg analyses the results of the wētā surveys we conducted during the summer 2025/26. For the first time in over 30 years, WCCT volunteers searched Price Basin again in February 2026. The results are grim, as our detection rate was 97% lower than that recorded by Gibbs, Heine and co-workers in April 1992. In March 2026, we also searched the head cirque of the Neale Burn in Fiordland National Park, where herpetologists had found two adult male Deinacrida pluvialis three years prior. Unfortunately, we were unable to confirm the existence of a giant wētā population in Fiordland. Not only did we fail to find wētā, but we also detected rats (Rattus spp.) in the alpine environment. Rats have caused the extinction of giant wētā populations in places where they have become established.
Southern Alps giant wētā Deinacrida pluvialis encounter rate (measured as number of wētā found/person-hours searching) during surveys at three localities in New Zealand’s South Island. Note the logarithmic scale—all values were increased by 0.01 in order to plot zero finds. Key: gray shapes = Neale Burn, Fiordland; blue shapes = Matukituki River West Branch; red shapes = Price Basin, Whitcombe River. Round shapes = day searches (turning rocks); diamonds = night searches (spotlighting). Full shapes = searches carried out precisely at the same site as the original survey in the same valley; empty shapes = searches carried out at different sites within the same valley. Crossed shapes = dead wētā are included in the total count. From (Hegg 2026).
No other giant wētā surveys in the Southern Alps have been documented. In spite of the small amount of data available, our surveys spanning a range of 240km across the South Island mountains paint a very consistent picture. There is no doubt that giant wētā in the alpine regions are experiencing a severe decline.
Surveys for alpine wētā are challenging. The environment is difficult, both because of the rugged terrain and because of the inclement weather in the South Island’s western regions. The species name “pluvialis” does, after all, mean “associated with rain”—a very apt name for this remarkable insect. Travel to the survey sites is by helicopter and is expensive. Survey methods used historically are not suited to the very low population densities we are now encountering. Better and more reliable survey methods are needed. When one or two wētā are all we find during four days of searching, there is simply not enough data to conduct meaningful statistical analyses. The vulnerability of giant wētā to all introduced mammals (mice, rats, stoats, cats, hedgehogs, and possums) complicates matters further, as removing of one or two predator species does very little to help the wētā.
Future steps will include surveys at additional locations in the Southern Alps, and determining what level of predator control is required to prevent the decline of alpine giant wētā populations.
The Wētā Conservation Charitable Trust would like to thank the volunteers who braved the elements and helped us with the 2025/26 surveys. Search teams included WCCT trustees Danilo Hegg, Maddy Pye, and Emma Gregg, and volunteers Kathryn Knightbridge, Lily Duval, Jolyon White, and Mikeely Milligan. Thank you also to Twin Needle for supporting us with field equipment.
Research article:
