How a Giant Australian Stick Insect Fooled Scientists for Decades

One of Australia's most frequently photographed giant stick insects spent roughly 50 years under the wrong name. A taxonomic revision published in Austral Entomology has revised the genus Anchiale, showing that specimens long treated as a single known species represent several distinct insects.

Led by Dr. Braxton Jones, a postdoctoral research associate at the University of Sydney, the study expanded the number of recognized Australian Anchiale species from two to five. The team formally named two new species, Anchiale robusta and Anchiale mabiensis, and reinstated a third, Anchiale albopunctata, after decades without formal recognition.

A 50-Year Misidentification

For decades, Anchiale robusta was conflated with Anchiale briareus, a species assigned to the genus Ctenomorphodes before a 2007 generic reassignment. The earliest documented confusion dates to 1976, when egg cases of A. robusta were cataloged as A. briareus. Because both share similar leaf-like camouflage, field naturalists and researchers routinely grouped them together.

The insects are substantial in size. Adult female Anchiale robusta measure between 12 and 16 centimeters in body length, while males reach 9 to 10 centimeters. "Males are always smaller than females – it's incredibly rare for a female to be able to still fly because they are quite heavy with … eggs," Dr. Jones said.

"Taxonomy is often a bit like detective work," Dr. Jones noted. "Even among some of Australia's most photographed and frequently reported insects, we're still finding species that have escaped scientific recognition."

Clues from Eggs and DNA

Field observations first alerted researchers to inconsistencies in the records. "When we went out into the field, and we saw a whole bunch of different individuals that looked morphologically different, and they were also living in … different habitats, that was our first hint that there was a bit more of a complicated story here," Dr. Jones said.

To resolve the relationships, researchers examined 35 Anchiale museum specimens, evaluated 37 non-Anchiale insects for comparative anatomy, and performed DNA analysis on 32 specimens. They also reared live specimens in captivity to monitor life cycles and collated roughly 1,100 citizen science records from iNaturalist and the Atlas of Living Australia.

Egg morphology provided a key diagnostic breakthrough. The newly described Anchiale mabiensis produces eggs with a distinctive lid-like cap featuring concentric rings, an egg architecture not previously recorded in this group of stick insects.

Fragmented Habitats and Conservation

The study also highlights conservation vulnerabilities. Anchiale mabiensis, whose females measure between 11.5 and 16.3 centimeters, lives in the critically endangered Mabi rainforest on northern Queensland's Atherton Tablelands. As of 2021, only about 1,050 hectares of that ecosystem remained.

Accurate classification provides practical utility for land managers. Stick insects can undergo rapid population increases that cause localized canopy defoliation, making precise species identification essential for monitoring potential agricultural and forestry impacts.

The authors reported evidence of a possible third undescribed species in the genus, though naming it requires additional specimens. Dr. Jones emphasized that documenting these species remains urgent: "These findings demonstrate the importance of protecting threatened ecosystems and documenting Australia's extraordinary biodiversity before we lose species without us having even discovered them."