"In the areas where we found the largest infestations, we've got a nice community effort where they are spraying weekly," he told The Maui News.

But there is a concern that the infestation on Maui that was first reported in July is not restricted to Haiku.

"I'm not completely convinced that Haiku is the only place on Maui that's got them. There's no reason for the caterpillars to be found only in that area," he said. "I was expecting to see them in other low-lying areas where there are developments that are bringing in plants from the Big Island."

The nettle caterpillar is the larva of a small moth, Darna pallivitta, native to Southeast Asia. It was was first discovered in Hawaii in palms being grown in a nursery on the Big Island in 2001. The state Department of Agriculture reported two caterpillars were discovered in Haiku in July.

Since the initial report, traps set to capture the moths have determined the nettle caterpillar is being found across the lower Haiku area, said Fukada, an entomologist with the Maui District office of the Department of Agriculture.

Both the moth and the caterpillar are small. The moth is about half an inch long while the caterpillar may grow to about an inch in length. The caterpillar has a dark stripe running the length of its back but is most noted for the bristly spines that cover its body. The moth is brown with a darker edge along the back of its wings.

The caterpillar is considered a serious pest because a large infestation can cause damage to the plants on which it feeds and because the caterpillar can cause painful stings when someone touches its spines.

Fukada said he tested the sting on himself, just so that he could better explain the threat of the pest. He described it as similar to the sting of a Portuguese man-of-war, noting that the toxin from the caterpillar's bristling spines apparently does not penetrate the thicker pads on the palm of the hand. It will cause a reaction on the skin on an arm or on the back of the hand.

He said there have been no reports of anyone suffering serious injury from contact with the caterpillars on Maui. There still remains a concern that as the infestation spreads, it will have an effect on agricultural operations, both on nurseries as well as with other types of farming.

"One of the disturbing things about what we're seeing in Haiku is that they're feeding on guinea grass. That means every pasture, every gulch, every old pineapple field can be infested; and that makes it much harder to control," he said.

He said there is a seasonal pattern to the infestation, with more of the caterpillars seen during the summer months. He also said the moths are not strong flyers, so they normally would not easily expand their range and could not spread among the islands unless they are transported on plants carrying the larva or eggs.

The caterpillars most often will be found on plants in the lily family, which includes the Hawaiian ti, as well as palm trees, lilies and mondo grass, which is also known as lily turf.

"But they're starting to see them on other kinds of plants on the Big Island," Fukada said.

Teya Penniman with the Maui Invasive Species Committee said her agency is deferring to the Department of Agriculture on dealing with control, but she said MISC is hoping there will be an aggressive control strategy to prevent the moth and caterpillar from spreading beyond the current infestations.

"We do not know how widespread it is. The department does have a plan to determine the extent of the infestation," she said. "We're glad that some landowners are taking steps to control the infestations they are finding."

She said she understood there is a study on bacteria that may control the larva, noting she supports control methods that are less harmful to the environment.

"Most people would rather use a benign control method," she said.

She and Fukada noted that many people would not be aware if there were an infestation in their yards until they found major damage on their plants.

"The moth itself is quite small, and it is hard to detect," Penniman said.

"There could be lots of them in other places," Fukada said. "It seems that people don't notice them until there are millions of them. Unless you're working with plants a lot, you won't notice the caterpillars."