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September 2008


Costa Rican Caterpillars – Cryptic, Caustic (sometimes) and Crucial to the Environment
Change one thing and you may change everything. It could be one of the by-laws of a rainforest ecosystem.

"Try and Find Me!" A cryptic Adelpha sp. (Nympahalidae) caterpillar. Photo courtesy of H. Garcia Lopez

Grant Gentry examines caterpillar leaf damage.

Caterpillar leaf damage.

Caught in the Act - Peacock Caterpillar Apatelodidae
Want proof? Ask the intrepid team of tropical entomologist Grant Gentry (Samford University, AL) and Lee Dyer (University of Nevada in Reno). They study caterpillars and the species that feed on them, in the rainforests of Costa Rica.

Dyer observed one such domino effect by simply adding some beetles to a pepper plant. “There’s the plant itself, and then there’s these little caterpillars that can actually kill the plant. And then there are these ants that live inside the plant that kill the caterpillars. And then there's a beetle that kills the ants. The experiments that we did, for the most part involved adding beetles to patches of plants where these beetles didn't exist. When we did that what happened is they suppressed populations of ants, which normally suppress the caterpillars. So with the ants gone, caterpillar populations exploded and the leaf biomass declined really quickly of this plant.” Having eaten through the pepper plants, the caterpillars moved on to other foliage, including seedlings of what might have become 100-foot trees.

To appreciate ecological diversity, look no further than the ubiquitous caterpillar. Worldwide, there are about 170,000 unique caterpillar species. Dyer and Gentry say they discover at least one new caterpillar each season they spend in the rainforest. Caterpillars are the wormlike larvae of butterflies and moths, and they’re voracious eaters of leaves. Despite their omnipresence, though, actually finding these critters can be tricky. During daylight hours in particular, caterpillars are often in hiding from wasps, flies, and other predators. “Very often they’ll eat and run, says Gentry. “So when you see (some leaf damage) you want to look at some leaves around it. And then I would suggest looking along the stems, and along the trunk, and... down around the base of the tree. And very often, you’ll find them hiding down there.”

Hiding from wasps is a smart move, considering the gruesome way in which these insects can cannibalize a caterpillar. Wasps use what’s called an ovipositor, kind of like an on-board syringe, to inject caterpillars with wasp eggs. When these eggs hatch inside the caterpillar, wasp larvae parasitize their ill-fated hosts. “The larva consumes important tissue inside the caterpillar,” Dyer explains, “and they grow along with the caterpillar. As the caterpillar is eating, the wasp larva is eating. But then when they get old enough, they need to pupate. Then they eat everything. They eat the brain; they eat the heart; they eat all of the insides of the caterpillar. Sometimes literally thousands of them will come popping out of a caterpillar.”

Parasitoids are not all doom and gloom for the wider ecosystem, however. If it weren’t for caterpillar-inhibitors like these, not much would stand between forest foliage and the relentless onslaught of countless caterpillars.

Hiding is not the caterpillar’s only defense, however. Some species are “visually cryptic,” meaning their coloring camouflages them within their surroundings. Others are “behaviorally cryptic,” in that they mimic the movement (or stillness) of the things around them. Caterpillars can also be quite toxic, possessing an arsenal of chemicals to keep would-be attackers (and scientists) at bay. Gentry recalls when Dyer handled a well-armed individual. “It was bright day-glow green. It had a big patch on its front that looked like a giant ant’s head. And Lee’s letting it crawl on him and kind of poking at it. And all of a sudden it sort of explodes in his hand. His hand was just coated with this stuff that started to burn.”

Most caterpillars in the US don’t sting – or explode with toxic spray – but always best to proceed with caution when handling an unfamiliar species!

If you’re interested in participating in caterpillar research in Costa Rica, click here!

See what Jim Metzner has to say about searching for Costa Rican caterpillars! Click here to read his blog.

Links to related stories:
Science Diary: Caterpillars - Many Types
Science Diary: Caterpillars - Alien
Science Diary: Caterpillars - Parasitoids
Science Diary: Caterpillars - Secrets of Finding
Science Diary: Caterpillars - Microcosm
Science Diary: Caterpillars - Interactions
Science Diary: Caterpillars - Importance of Diversity
Science Diary: Caterpillars - Stingers
Science Diary: Caterpillars - Cryptic
Science Diary: Caterpillars - Frass Thrower

Today we weren't planning to launch 'Mind Alphabet Films'. Today we were definitely going for 'off'' and left the camera at home.

Then nature strikes back. So now, we resort to old fashioned imagery-- verbal description:

1. Gorgeous mother wild-turkey, with its one baby, magnificently cutting across the backyard -- spreading its wings and plucking berries.
2. Deer, bouncing out of a wheat-field where it was perfectly camouflaged - 'We can't draw such thing!' - bouncing, showing its white tails - in the orange-red, hip-high wheat.
3. Sleepy baby squirrel, palm-sized -- half-asleep, snuggled into the crook of a lower branch of an enormous oak tree, its tail perfectly outlining the beautiful wave of its little spine in fluffly tail-fur.
4. Sparrow babies, chirping for their parents from a newspaper/mail box -- really? we looked in, carefully -- must have been three of them in a cozy nest. We hope the paper-delivery notices. Wow.
5. Firefires showing up en masse. Blinking silent lights everywhere.

Our camera's video caught few flickles and tints. But that's about it. One photograph kind of made it but not that great at all.

But today was the day, nature was at its peak. Hot heat waves and then down-pouring rains and then cool breeze - a thing to remember - in terms of 'Circles and Lines' - how we have this cue about American nature.