On a mission to scout out rare snails in a Maui forest, botanist Keahi Bustamente hopped out of a helicopter into the Olowalu Valley last year and began tracking a rain-swollen stream bed blooming with native mamaki.
That’s when he saw it: A black and orange-speckled caterpillar with bright white hairs gorging on a light green mamaki leaf.
Bustamente marveled at the creature measuring about the same length and girth as his ring finger, far larger than the caterpillars belonging to any of Hawaii’s indigenous moths and butterflies. With its striking size, bright markings and a peculiar habit of spitting green juice extracted from the veins of leaves, it was different from anything Bustamente had ever seen in Hawaii.
The Ramie caterpillar has begun to invade nettles plants on Maui, threatening both native plants and indigenous moths and butterflies.
“We were hoping it would be some rare endemic caterpillar,” said Bustamente, who brought it home to see what form it would metamorphosize into. “But we weren’t that lucky.”
What Bustamente had discovered was the nation’s first documented sighting of a Ramie caterpillar in the wild. Since he identified it and it grew into a Ramie moth, scientists across Maui have called in additional sightings of the unwanted and potentially damaging species in both arid ranchlands and wet, mid-elevation valleys.
“It was disheartening,” said Bustamente, an invertebrate biologist with the Department of Land and Natural Resources’ Division of Forestry and Wildlife.
Native to Asia, the Ramie caterpillar and moth poses a new threat to indigenous moths and butterflies on Maui, including the imperiled Kamehameha butterfly. That’s because it now joins hundreds of Hawaii’s native insects in competition for food from plants in the nettles family.
“When something new comes in, all of these species that belong here now have to compete.” — Keahi Bustamente, DLNR biologist
Additional hazards to Hawaii’s native moths and butterflies come in the form of habitat destruction and the introduction of invasive predators like parasitic wasps, which have already made the Kamehameha butterfly a rare sighting. Found nowhere else on Earth, it is the state’s salient ambassador for all native insects. And it is one of only two endemic butterflies in Hawaii.
The fresh threat of the Ramie caterpillar and moth doubles down on the difficulties that the Kamehameha butterfly and other native insects face. It also poses a problem for their host plants, including 14 species in the mamaki family that are found only in Hawaii and are in some cases critically endangered.
In addition to being food sources for native insects, mamaki is a plant species steeped in cultural importance. With fibers stronger than the wauke plant, mamaki is a prime source for kapa. Its leaves are used to make an invigorating tea with medicinal qualities.
The Ramie caterpillar’s arrival is a problem for the perpetuation of these cultural activities even though mamaki is still commonly found in wet forests and valleys.
“A lot of the plants we now consider to be rare or critically endangered were at one time common and found across all the islands,” Bustamente said.
It’s unclear how the Ramie caterpillar and moth came to Hawaii and scientists are still trying to ascertain how damaging its arrival could be. But Bustamente warns that the introduction of alien species to new territories is one of the principle threats to native wildlife.
He said his most recent encounter with the Ramie caterpillar spells out the harm it’s capable of inflicting on Hawaii’s ecology.
“The last time we saw them, we removed 100 caterpillars from one branch of mamaki,” Bustamente said. “That can devastate a plant. And it’s also competing now for food with native moths that are already having a hard time.”
Hawaii’s Kamehameha butterfly, found nowhere else on Earth, is struggling to repopulate in the face of challenges that include habitat destruction and an invasive parasitic wasp. Now there’s a new threat: the Ramie caterpillar and moth.
Bustamente said he brought home the 100 caterpillars and fed them an array of native plants to test the limitations of their palates. They ate the plants, he said, but all but three died before achieving metamorphosis.
The Ramie caterpillar and moth has already established itself in new populations outside its native habitat after people spread it into the Philippines, Japan, Australia and New Zealand, according to the DLNR. Now Maui joins that list, and scientists working with Hawaii’s native plants and insects outside of Maui are on alert for signs of dispersal to new islands.
Bustamente is mapping the Ramie caterpillar’s Maui dispersal. It’s a species that can spread with the wind, and it’s also possible that people could transport its eggs from Maui to new islands on the leaves of plants.
There are many unknowns. But Bustamente said he’s fairly certain that the moth and caterpillar’s arrival on Maui is probably not an accident. He said it’s important for people to understand how the introduction of one exotic species can cause dramatic and often unstoppable consequences.
“In Hawaii, 99% of the plants, animals and things that are here are only found here,” Bustamente said. “When something new comes in, all of these species that belong here now have to compete. I know there are a lot of people who are like, ‘How did this slip through the cracks?’ More people need to be active in voicing their concern and actively protecting where we live.”
Ramie caterpillars are black and sometimes yellow, with bright orange-red spots and white hairs. Kamehameha butterfly larvae are black when first hatched, and greenish when ready to make a cocoon.
Their behaviors also differ.
To scare off birds and other predators, the Ramie caterpillar rears up onto its hind feet and waves its body around.
“When it’s trying to scare off predators, this thing is fuzzy, colorful and rears up its head and waves it around, and it spits,” Bustamente said. “Kamehameha caterpillars don’t do that.”
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