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An Inordinate Passion for Tropical Moths

National Geographic grantee Professor Roger Kitching wants to know how much less diversity there is in tropical rainforest that has been logged than in unlogged “primary” forest. He finds some clues from the moths he draws to his lamp, Stuart Pimm reports in words, images, and video from the field, deep in the Borneo jungle.


Photo by Stuart Pimm

By Stuart L. Pimm
Special Contributor to NatGeo News Watch

Borneo, Malaysia–Nothing quite captures the idea of “biodiversity” than standing in front of a white sheet lit by a mercury vapor lamp in the equatorial jungle at night. Mercury vapor lamps emit a lot of ultraviolet light which seems to be particularly attractive to moths.

Even though the sun has set, it’s still hot, the humidity is 100 percent, sweat drips down our faces and into our eyes, making the mill of flying insects into our faces even more annoying.


National Geographic grantee, and Griffith University Professor of Ecology, Roger Kitching keeps up a running commentary on the insects as they land on the sheet. “That’s a plecopteran–stone fly, and that’s a stinging nocturnal wasp–don’t let it get in your hair. Catch that one! We need to identify it.”

This light trap is in the middle of the largest remaining fragment of tropical forest in Borneo, the Danum Valley.

We’re here to teach a group of undergraduates from Griffith University in Brisbane, Australia about the basics of tropical rainforest natural history.

Photo of Roger Kitching
by Stuart Pimm

Before this course, Roger had been here to ask a particular question, one with important implications for protecting global biodiversity.

The field center accommodates not just us, but an enthusiastic set of visitors who come to the forest to enjoy its wildlife.


Over the last ten days, we’ve seen five species of monkey. Pig-tailed macaques feed around the center; their small young generate whoops of pleasure from their undergraduate audience as they play in a nearby fig tree, grabbing fruit from branches their parents cannot reach.

It’s the gibbons that have everyone getting their cameras and, on several days, the orangutans. They are close enough to us evolutionarily that it’s hard not to read human interpretations into their behaviors and expressions.

Photo of maroon langur
by Stuart Pimm

When one makes a tree-top nest in which to sleep for the night just opposite the center’s open dining room, our loud chatter turns to whispers. We wouldn’t want to disturb its sleep.

With every day, we add to our list of birds, mammals, lizards, and frogs. And every night, small groups go out with spotlights to add to the totals those species that only emerge at night.

Exciting though these vertebrates are, Kitching’s focus on insects–and moths in particular–is deliberate.

The Danum Valley is a large tract of “primary” or largely unlogged rainforest. Surrounding it, however, are large areas of “secondary” forest–forest that has been logged, sometimes extensively, and which is re-growing–either on its own or with some help with replanting.


Photo by Stuart Pimm

Kitching’s question is how these two kinds of forest differ.

Everyone expects there to be fewer species in the secondary forests.

How many fewer is the easier of two questions. One counts the species in primary and secondary forest–and compares them.

Ecologists call these counts “alpha diversity”–they are measures of how many species there are at a particular place.

Kitching could do this easily–running his sheet and UV light in primary and secondary forests close to the center.

The second question is the more difficult one. “We need to know beta-diversity–how much turnover there is from place to place.”

Watch Stuart Pimm’s video report:

Video copyright Stuart Pimm

Kitching explained the general idea that logging tends to homogenize the forest. Just as you can get the same hamburger in New York, London, Beijing and even Borneo, so in secondary forest the same species may occur everywhere.

“Moths are a good test of this–because they are herbivores that are tied to specific plant species. They reflect the likely homogenization of the logged forest–the fact that only a few common tree species survive in the canopy there.”


The primary forest, in contrast, is more variable from place to place with a sometimes bewildering variety of tree species making up its dense canopy.

So, for the last two years, Kitching has trapped moths at sites in primary forest separated by 100 meters (yards), to 60 kilometers (40 miles) apart and a similar set in secondary forest. At each site, he identifies the first one thousand individuals to species–and there are a lot to choose from.

“We have firm estimates that there are nearly 4,000 species of the larger moths around Danum and perhaps 10,000 species in Borneo as a whole,” he says.

“And the answer, Roger?” I asked. “You have to wait for that, we’ve only just finished counting and identifying all those species!”


Photo by Stuart Pimm

Professor Stuart L. Pimm is a conservation biologist at Duke University, North Carolina. A former member of the National Geographic Committee for Research and Exploration, Pimm is the author of dozens of books and research papers, including the book “The World According to Pimm: A Scientist Audits the Earth.”

Read earlier blog posts by Stuart Pimm:

Florida Panther Fights for Survival Again–This Time in Washington D.C.

Many Mammal Migrations Are at Risk of Extinction, Research Finds