A boy eyeing a caterpillar in Tanjung Duren, West Jakarta, where thousands
of the prickly insects have infested pine trees
Unpredictable weather coupled with a decline in natural predators is responsible for a recent plague of caterpillars in parts of the country.
Though the phenomenon is centered largely in Probolinggo, East Java, smaller reported outbreaks in Central Java, West Java, Bali and, most recently, Jakarta have prompted fears of a widespread infestation.
But Aunu Rauf, an entomologist at the Bogor Institute of Agricultural (IPB), says there is no connection between the outbreaks in Probolinggo and those in the other areas.
“There are at least 120,000 types of caterpillars in the world, so those found in Bekasi [West Java] and Probolinggo would be different from each other,” he told the Jakarta Globe on Wednesday.
“I’m sure the ones in Tanjung Duren [West Jakarta], where people have claimed to have been ‘attacked’ by caterpillars, are also a different type.”
Since March, millions of hairy caterpillars have cropped up in at least five subdistricts in Probolinggo, invading fields and homes. They have also caused itchy rashes among residents.
The caterpillars have also destroyed more than 8,800 mango trees — the district’s main agricultural produce. However, the caterpillars in Bekasi were found largely in bushes, while those in Tanjung Duren were found on pine trees.
“Basically, in the life cycles of pests, it’s normal for them to increase in number at the start of the dry season — especially caterpillars,” Aunu said, adding that the country was currently in the transition period to the dry season.
“In the current case, however, their numbers exploded because of the prolonged rainy season last year that disrupted [the population growth of] natural predators, particularly birds and other insects.
“In addition, parasitoids, insects similar to wasps whose larvae live within caterpillars as parasites, are for some reason on the decline. Their role as the caterpillars’ natural enemy is very important because they lay their eggs inside the caterpillar, and when those hatch, the larvae eat up the caterpillar from the inside.”
Aunu said the outbreak in Probolinggo, coming 70 years after the last similar outbreak there, was remarkable only for the extent of the damage being caused to mango trees.
“These caterpillars have had a tremendous effect — not only economic, from eating all the mango leaves, but also social,” he said. “Because now the villagers are afraid to carry out their regular activities due to all these insects coming into their houses.”
Aunu said while it was good for people to be aware of the caterpillar phenomena, including in Tanjung Duren and Bekasi, he stressed it was normal for the caterpillar population to increase at this time of year and should not cause too much concern.
“If these caterpillars were the type that run around fields or enter homes instead of clinging to tree branches, then we would have to take action,” he said.
Hari Sutrisno, an entomologist from the Indonesian Institute of Sciences (LIPI), said that as long as the caterpillars were not harming people, they should be left alone.
“There’s been quite a frenzy over these caterpillars, and it’s all a bit too much,” he said, adding that the reports from Bekasi were particularly exaggerated. “Caterpillars don’t claim lives.”
Hari said the best way to deal with the insects was to collect them for incineration rather than use pesticides on them.
“Another method is to blend dead caterpillars with water and spray it on the live ones,” he said. “The spray acts as a natural insecticide because caterpillars that die naturally usually contain a virus that’s deadly for the species. It’s a lot better than using pesticides, which can have a long-term impact.”
Aunu also cautioned against using pesticides. “Just pick them off the tree branches and get rid of them,” he said.
“Don’t use pesticides because you don’t know what other kinds of insects you’ll be killing that serve a function for the tree.”
In the Probolinggo case, Aunu said the caterpillar numbers were already declining because most of the insects had already turned into butterflies.
“The only way to deal with them is still through their natural enemies,” he said.
“To do this, put caterpillar pupae into a jar and see whether they become butterflies or wasps. If they turn into butterflies, then we need to kill them. But if you get a wasp, that means they need to be released because parasitoids are present and functioning.”
Darmuna, a resident of Tanjung Duren, said the problem was that the hairs of the dead caterpillars were being blown around by the wind and making people itchy.
He added that the outbreak was not a new problem, with a similar event taking place in 2007.
Sholeh, deputy head of a neighborhood unit in Tanjung Duren, suggested the best way to get rid of the pests would be to chop down the 29 pine trees along Jalan Sekretaris on which they were gathered. He also said the trees needed replacing because they were old and several had been uprooted during rainstorms.
“We expected the city administration to take our opinion seriously and take action on this case by chopping down the trees and replacing them with new ones,” he said. “Instead, they just sprayed the lower parts of the trees [with pesticide].
“Every day we have to deal with the hairs that make us itchy. We could chop the trees down ourselves, but it’d cost Rp 300,000 [$35] per tree and there are 29 of them. Besides, the administration already has a budget to chop down trees.”