Jumping caterpillar navigates by sun

August 21, 2013
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Calindoea trifascialis caterpillar in a leaf

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Watch the leaf-wrapped caterpillar in action.

An unusual caterpillar uses the sun to navigate as it jumps to safety, according to scientists.

The larva of Calindoea trifascialis, a species of moth native to Vietnam, wraps itself in a leaf before dropping to the forest floor.

It then spends three days searching for a suitable place to pupate, despite not being able to see out of its shelter.

Experts found the insect used a piston-like motion to jump away from strong sunlight.

“We believe the object of the jumping is to find shade – to avoid overheating and desiccation,” explained Mr Kim Humphreys from the Royal Ontario Museum, Canada who conducted the research alongside Dr Christopher Darling.

Their findings are published in the Royal Society journal Biology Letters.

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Although Mr Humphreys described the caterpillar as “non-descript” in appearance, he said its behaviour makes it unique in a number of ways.

“Caterpillars or larvae that jump are rare in themselves,” he said. “[This] caterpillar is remarkable for its jumping, which no other insect does in this way. It also makes its own vehicle [or] shelter to jump in.”

“It is also the only one I know of that jumps in an oriented way.”

C. trifascialis is found throughout South East Asia and researchers were initially studying the caterpillar’s defence mechanism in Yok Don National Park, Vietnam.

It secretes a pungent-smelling toxic fluid from glands behind two arm-like protrusions to protect itself from ants.

After storing a number of caterpillars under his bed, Mr Humphreys woke the next day to a “thumping” sound as the leaf-wrapped larvae tried to jump out of their plastic container.

“I was absolutely struck speechless when I first saw this,” he said.

To understand why the caterpillars jumped, the researchers studied them in the lab. Constructing transparent leaf rolls from plastic allowed them to see how the insects moved inside their shelters.

To jump, the caterpillar anchors its rear prolegs to the floor of its shelter and lowers its head. Its front section then suddenly moves backward, causing the animal to arch upwards.

Calindoea trifascialis caterpillarThe caterpillars have arm-like protrusions for spreading toxic fluid

Its back strikes the ‘ceiling’ of the shelter, causing the whole structure to jump backwards.

Field studies showed the caterpillars moving in this way for around three days.

Previous studies have suggested that larvae jump to avoid predators, parasites or sunlight.

In their research, Mr Humphreys and Dr Darling found that the jumping caterpillars were safer from predators when they fell to the ground but were then vulnerable to overheating in sunlight.

Further tests identified that the caterpillars jumped away from the most intense light source when in their shelters, suggesting that their unusual behaviour relates to improved survival as they head for a shady spot to pupate and transform into a moth away from predators.

“Imagine you are lost in the forest with a limited supply of water. You know somewhere around there are roads that will lead you to safety – you can’t see where though, because there are so many trees. You have no map, but you have a compass,” said Mr Humphreys.

Calindoea trifascialis mothThe caterpillars pupate to transform into moths

“To get to safety, should you wander around, hoping to chance on a road? Should you use the compass and just go straight in any direction? Or should you do something in between: a little random, a little straight? This is something like the dilemma the insect has to face.”

Mr Humphreys said the research is valuable from an evolutionary point of view because this vulnerable “wandering phase” is subject to “significant natural selection”.

“I think caterpillars are understudied and underappreciated compared with their more photogenic adults, the moths and butterflies,” he said.

“Perhaps there are interesting aspects of the biology of other larvae that are remaining to be discovered. This caterpillar and its moth were known to science before, but no one has seen this behaviour until now.”

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