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A Newly Discovered Caterpillar Makes a Deadly Fortress of Its Cocoon

Scientists have found a caterpillar in a Borneo forest that uses toxic tree resin to build an extra-safe home for its metamorphosis

Resin, similar to the kind shown here, is used by the newly discovered caterpillar to build its cocoon. (Ned Therrien/Visuals Unlimited/Corbis)
smithsonian.com

One little insect in Borneo is taking home defense to a whole new level.

Scientists have discovered a caterpillar that uses tree resin—rather than the more commonly used silk—to build a hard, multi-walled, possibly poisonous cocoon. “No other butterfly or moth is known to make a cocoon from such material,” BBC Nature reports.

The as-of-yet unnamed caterpillar is bright red and scattered with tall black hairs. Observations recently published in the Journal of Natural History indicate that when it gets ready to pupate, it heads over to the bark of a plant species called Vatica rassak. There, it uses the tree’s sticky sap-like resin to construct a cocoon engineered to keep out unwanted guests.

It creates a smooth interior wall that is then bound by silk to an exterior structure. The exterior is studded with sharp spikes made of flakes of resin, which dry over time and appear almost like shards of broken glass. The caterpillar’s new home is further weaponized by the toxic, potentially deadly properties of the resin.

Professor William Symondson of Cardiff University, who discovered the remarkable caterpillar told BBC Nature:

“It is a wonderful piece of evolution, because the resin is highly toxic and it makes you wonder how this species of caterpillar first started to use such a dangerous material.

“Relatives of this moth make cocoons out of pieces of bark and therefore it is likely that individuals that first built in a proportion of resin into their cocoons, as well as the bark, survived better. The resin not only hides the pupa well but also any inquisitive predator, bird or insect, has to get past a highly toxic barrier. Few are likely to be able to do so.”

Symondson made the find while leading students on a research expedition through a Bornean wildlife preserve, where Cardiff University has a field station. However, though the team documented the cocoon-making stages of this first specimen, searches have yet to uncover another example of this caterpillar, preventing scientists from pinning down its taxonomic identity. Symondson told the BBC that he hopes to soon find a resin cocoon with the pupa still inside so that researchers can watch to see what kind of butterfly or moth emerges from the fortress. 

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