An invasive caterpillar species, the ramie moth (Arcte coerula), known for its voracious appetite for native Hawaiian plants, has been sighted on Kauaʻi, marking the first instance of its presence on the island. A concerned citizen's report to the Kauaʻi Invasive Species Committee (KISC) last month led to the discovery of a live caterpillar, sparking a collaborative response effort among various agencies.
These efforts include the Division of Forestry and Wildlife (DLNR), KISC, the Hawaiʻi Department of Agriculture, and Biosecurity, alongside the University of Hawaiʻi at Mānoa, according to a recent report from DLNR. The ramie moth caterpillar, which begins life at a tiny 1/16 inch, can grow up to 4 inches long, and is particularly destructive to māmaki plants and other native nettles such as maʻoloa and ōpuhe, which are crucial to the ecosystem and native species like the Kamehameha butterfly and native snails.
The ramie moth is no stranger to Hawaiʻi, with the first detection on Maui in 2018, followed by sightings on Hawaiʻi Island in 2020, and recently on Oʻahu in 2025. While the recent find on Kauaʻi involved just one caterpillar, officials warn that the species can spread quickly, both through movement of host plants and the flight capability of adults, aided by air currents.
The community is urged to assist in early detection efforts by reporting sightings of ramie moths or their caterpillars on māmaki or other host plants, "Please take photos and report the sighting immediately to 643pest.org," stresses the DLNR report. This measure is critical to avoid the rapid island-wide spread, and to protect native forests from potential devastation. The caterpillars of the ramie moth are distinguished by their green to yellow and black coloration, sporting bright orange-red spots and thin white hairs, while adult moths are dark brown with black and silver markings, with a wingspan of up to 3.5 inches.
