mamaki pest — Maui Invasive Species Committee (MISC)

In 2018, an invertebrate biologist discovered an unfamiliar black caterpillar feeding on a māmaki plant in Olowalu Valley. Experts confirmed the caterpillar was ramie moth, a species native to Southeast Asia that aggressively feeds on plants in the nettle family, like māmaki. The biologist’s sighting marked the first confirmation of ramie moth in Hawai‘i and the U.S. Soon, a flood of reports from around Maui indicated that the pest was already too widespread to control. Ramie moth was later detected on Hawai‘i Island in 2020 and O‘ahu in 2024.

Ramie moth caterpillars can be identified by their coloration – black with orange dots and white hairs – as well as their behavior – they “hiss” when approached. Photo: DLNR

Initially, experts feared that ramie moth could devastate māmaki and other native nettle populations, putting a valuable cultural and environmental resource at risk. However, while the moth remains a threat, new research suggests that natural enemies may be lessening the impact on Maui and the other Hawaiian Islands.

When a new pest arrives to the islands, it takes time to understand how it may interact with the environment. Hawai‘i’s ecosystems are unlike anywhere else on earth. New pests are suddenly sharing space with species they’ve never encountered before. Predicting how a new species will behave in the islands takes research, monitoring, and time. Michelle Au, an entomologist with the College of Tropical Agriculture and Human Resilience (CTAHR) at UH Mānoa, has been studying ramie moth since its arrival to Maui with a focus on parasitism and predation rates in Hawai‘i for the last three years. “The bulk of my research is just trying to understand what predators and parasitoids are impacting the population, and seeing if it’s the right kind of mortality, these key mortality factors, that will actually control the population,” says Au. Her findings show something encouraging: predators and parasitoids already present in Hawai‘i seem to be controlling the ramie moth population.

According to Au, birds and parasitoids are the primary natural enemies of ramie moth larvae. Parasitoids affect most life stages of the moth, from egg to third instar larvae. “Egg parasitism is quite high,” says Au, roughly 50 to 60 percent in some areas. “Then there’s larval parasitism. There’s one larval parasitoid we’ve been finding…it’ll lay eggs on the caterpillars which feed and develop, eventually killing the ramie moth caterpillar host.” If the larvae escape parasitoids, they may become a tasty treat for birds.

While Au’s research is hopeful, ramie moth is still spreading, and it’s still a threat to māmaki. “[Ramie moth] will kill smaller plants, especially if it’s a young tree,” says Au. “If it completely defoliates the leaf, the tree may die.” Māmaki is a valuable cultural resource, prized for its medicinal and textile uses. It also supports a variety of native insects, including the happy-faced spider and pulelehua (Kamehameha) butterfly. Māmaki isn’t the only species affected by ramie: the pest also feeds on other native nettle species such as ōpuhe and endangered ma‘oloa.

Ramie moth larvae feed heavily on plants in the nettle family, like māmaki. Defoliation can kill a young or small māmaki. Photo: DLNR

While ramie moth’s impacts aren’t as devastating as originally thought, scientists like Au still face a myriad of challenges in understanding how the pest behaves in Hawai‘i. “It seems like as [ramie moth] spread, the biology is changing,” says Au, explaining that the moth’s expansion and season on O‘ahu differs from Maui and Hawai‘i Island. “If it gets to Kaua‘i, it may have a different biology. There’s still a lot we don’t know.”

Ramie moth is just one of the latest pest insects to establish in Hawai‘i. Its arrival underscores the importance of biosecurity in the islands. About 20 new insects establish in the islands each year. New pests may impact agriculture, recreation, or, like ramie moth, cultural and environmental resources. Some have little impact on the environment, while others become major pests, like coconut rhinoceros beetles and little fire ants. Preventing arrival and interisland spread provides the greatest benefit.
On Maui, Au encourages residents to stay alert and report sightings of ramie moth. Scientists like Au rely on public reports and live specimens for research. However, don’t confuse endemic pulelehua butterfly larvae with ramie moth. View the Hawai‘i Invasive Species Council’s ramie moth resources or the CTAHR ramie moth extension website for more information and identification tips. You can also email Michelle Au directly at ipmlab@hawaii.edu. To prevent further spread, avoid moving plant material, especially māmaki, inter-island. If ramie moth is seen anywhere on Maui, report it at 643pest.org or call 643PEST.

The caterpillar of the ramie moth can be identified by its coloration — black with orange dots and white hairs — as well as its behavior — it “hisses” when approached. Report sightings to 643PEST.org. — Department of Land and Natural Resources photo

Last October, Keahi Bustamente was looking for rare snails in Olowalu Valley when he noticed a māmaki plant showing signs that something had been eating it. A quick look revealed the culprit was a black caterpillar. He plucked the unfamiliar insect in hopes he had found something new – perhaps a native species. Bustamente is an invertebrate biologist with the Pacific Cooperative Studies Unit. He works with the Department of Land and Natural Resources and spends his days scouring the forests for native land snails.

He couldn’t identify the larva and started asking colleagues on Maui and Oʻahu. An entomologist on Oʻahu guessed that it was from a ramie moth, never before found in Hawaiʻi, but to confirm the identification, Bustamente had to raise the caterpillar to the adult moth stage. A brown and black moth with a 3-inch wingspan emerged – it was indeed the ramie moth.

This new moth, Arcte coerula, is native to the Philippines and dines on plants in the nettle family (Urticaceae). The moth is large and a strong flyer, but it most likely arrives on our shores as a hitchhiker. Uninvited, this interloper is now munching its way through māmaki in our forests.

Māmaki is traditionally used in Hawaiian culture for medicinal tea and cordage. Increasing interest in the plant has led it being grown commercially for tea. In the forest, māmaki serves to stabilize streambanks. Māmaki supports over a dozen species of native insects, including leaf miners, moths, and beetles, and the Kamehameha Butterfly, which is reliant on māmaki.

Māmaki supports over a dozen species of native insects [that are] reliant on the plant itself. — Department of Land and Natural Resources photo

It’s not just māmaki that is at risk. The caterpillar of the ramie moth has been found on other plants related to māmaki, including maʻaloa (Neraumdia sericea), an endangered plant on the verge of extinction.

A few weeks after the Bustamente found the caterpillar in Olowalu, a native-plant grower reported finding it in Olinda and ʻUlupalakua; sightings from Waiehu, ʻĪao Valley and the mountains of West Maui soon followed. It quickly became apparent that the ramie moth was already too widespread to be removed from Maui.

The ramie moth is only the latest in a host of pest insects. Every year, over a dozen new insects arrive in Hawaiʻi. Some turn out to be serious invaders forever altering life in the islands. Little fire ants, coconut rhinoceros beetle, varroa mite, coffee berry borer, and naio thrip are recent examples. These troublemakers threaten native plants and animals, the function of our environment, our relationship with nature. Once established, they impact cultural practices, recreation and the livelihoods of the residents of Hawaiʻi, jeopardizing tourism and agriculture.

“At any point, some new plant or animal can come in and forever change Hawaiian ecosystems in a way we can never recover,” says Bustamente.

The arrival of yet another pest highlights the need for increased prevention efforts. The Hawaiʻi Invasive Species Council in cooperation with state and federal agencies developed the Hawaiʻi Interagency Biosecurity Plan. The plan lays out specific steps needed to improve biosecurity in Hawaiʻi. The plan needs legislative support and funding to be implemented.

It’s still too early to tell what the impacts of the ramie moth will be, but Bustamente and others are concerned. “The caterpillar can hammer a māmaki plant,” says Bustamente, who has found over 100 individuals on a single plant. Even though it’s unlikely all will survive to adulthood, it’s during their caterpillar stage that they damage māmaki.

If you have māmaki or other nettle-family plants in your yard, be alert to the threat of the ramie moth. Look for a black caterpillar (sometimes yellow) with bright orange spots and white hairs. Be careful not to confuse the ramie moth with the native Kamehameha caterpillar. The Kamehameha caterpillar is green for most of its life but is black immediately after hatching. The behavior differs as well – the ramie moth caterpillar rears up and spits to defend itself. Report sightings to the statewide pest hotline, either by phone: 643-6245 or online: 643PEST.org. You can learn more about plans to improve Hawaiʻiʻs protection against the arrival of new pests at the Hawaiʻi Invasive Species Council’s website: https://dlnr.hawaii.gov/hisc/plans/hibp/

Lissa Strohecker is the public relations and education specialist for the Maui Invasive Species Committee. She holds a biological sciences degree from Montana State University. Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy, and quality of life.

This article was originally published in the Maui News on July 13th, 2019 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Kia‘i Moku: Ramie Moth Still Threatens Native Plants, But Natural Predators Offer Hope

Damage to māmaki plant by moth highlights need for biosecurity

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