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Why Do Poisonous Caterpillars Jump?

Chris Darling stuck out his tongue and licked the caterpillar.

It was 1998, and as a professor at the University of Toronto, Canada, this wasn’t Darling’s first foray into entomophagy. But it was his maiden taste of the caterpillar, a Calindoea trifascialis. The academic’s tongue responded unfavorably to the foreign stimulus and immediately went numb.

“You just pick [the caterpillar] up, and just dab it on your tongue like you’d taste fruit,” he said. “It didn’t really have any taste; it just sort of numbs the tongue.” (Also see “For Frog-Licking Scientist, the Tongue Says It All.”)

When Darling and his students began studying the yellowish-orange caterpillar, they noticed that their charge was secreting a strange liquid from its glands. Rather than wait for a lab test to determine the liquid’s composition, Darling decided to run his own experiment—licking it. The harmless numbness he felt meant that the caterpillar was fighting back with a “chemical defense.”

“I cajoled a couple of students to do it as well to make sure we had a replicated sample,” he said. He’d later identify the substance as a mixture of hydrocarbons and hydrogen cyanide, a poison that coats the insect’s torso.

Darling and Kim Humphreys, one of his former students, recently co-published a study in the journal Biology Letters on another facet of the bug’s fantastical abilities—jumping.

Jumping Blind

Jumping caterpillars are pretty rare, and scientists speculate that Calindoea trifascialis larvae jump to escape from the heat. Temperatures in their Vietnamese habitat can reach well over 95 degrees Fahrenheit (35 degrees Celsius), and that means trouble for an earth-bound insect.

jumping caterpillar
Calindoea trifascialis. Photograph by Kim Humpreys, Royal Ontario Museum

These caterpillars can jump dozens of times a minute to find shade, but they have no idea where they’re going, Darling said.

That’s because the caterpillars are jumping around with tents on their backs. When a caterpillar hatches, it uses its teeth to cut a hole in a leaf and then painstakingly pulls that leaf over its head and secures it with silk. The homemade tent fills with the stench of poisonous chemicals and protects the caterpillar from any would-be predators, like ants. (Also see “How ‘Zombie’ Virus Liquifies Caterpillar Hosts.”)

“You can imagine you’re inside this smelly, enclosed space,” Darling said. “When [ants] try to get into the tent, they basically get incapacitated. They get knocked out, stunned.”

Biomechanics of a Jumping Caterpillar

However, the tents also prevent the caterpillar from navigating effectively and require a lot of energy to carry.

“Everybody is interested in the jumping behavior just because that’s really cool,” Darling said. “It’s a significant amount of force to piston the body and the leaf.”

It gets better: The caterpillar actually jumps backward with its head facing away from its destination. The next step is to figure out why and study the biomechanics involved in a caterpillar jump, Darling said. (See more National Geographic bug videos.)

Perhaps while he’s at it, the professor will take the opportunity to repeat his old experiment and lick the caterpillar once more. After all, Darling admits to having a penchant for licking bugs.

“It wasn’t the first bug I’ve tasted.”

Comments

  1. Brad Shue
    USA
    August 31, 2013, 2:19 am

    Why do these studies in Canada when the lifespan of the caterpillars is so short and so few species compared to the lower US states?

    Kinda sounds like you want a lot of money for a little field work time and then you goof off for the rest of the year acting like you are analyzing data. At the end of this time you produce a substandard presentation and conclusion…. “worthy of more research”.

    Sounds like a pork barrel to me.