Pretty poison

Natural History, March, 2003 by Erin Espelie

To be seen or not to be seen? Most slug caterpillars survive their vulnerable youth by making a visual statement. Orange-tinted skin, black body rings, and piercing yellow eyespots mark the Vietnamese larva of Setora fletcheri pictured here. But this brazen display fades away with adolescence. First the flashy spikes collapse. Then a spherical cocoon is spun. The brown, mature moth finally emerges with a more conservative strategy: to blend in.

Not all of the slug caterpillar's decoration is just for show. At any sign of danger, each cluster of spines blooms into a bristly sphere. Glands at the base of the spines produce venom rich in histamines--liquid peril for any would-be attacker.

Photographer Mark Moffett stealthily approached this S. fletcheri in Tam Dao National Park, north of Hanoi, where the mountains rise from the fertile Red River Delta as "islands in a sea of clouds." The description well suits the numerous and distinct niches that isolate the residents of Tam Dao, making it a kind of untapped, continental Galapagos, teeming with exotic organisms. Trekking at twilight in the park, Moffett spotted this larva shining on the path. Even in the dark, he notes, it glowed "like a marine creature"--much too extravagant to resist.

Hark Moffett ("The Natural Moment" page 10) made his first foray into tropical rainforest research at the age of seventeen, catching snakes for a Costa Rican expedition led by naturalist Max Nickerson. Moffett continued to explore rainforest habitats as a graduate student at Harvard, where he studied under the evolutionary biologist E.O. Wilson. While doing his dissertation in biology, Moffett traveled for more than two years in Asia, teaching himself photography in his spare time. He has won international awards for his pictures, some of which were exhibited in twenty-five countries as part of the 1992 World Press Photo exhibition. He photographed the brilliantly colored slug caterpillar in northern Vietnam.