Some whistle, some look like snakes and others inflate when you yell at them, but deep in the rainforests of South America lives a caterpillar with a getaway tactic so strange it hardly seems possible. To avoid being eaten, this creature rides eternal, shiny and chrome. 

Image: Rubens Luciano/used with permission

Incubating inside this mirrored palace is Mechanitis polymnia, the orange-spotted tiger clearwing. And while it might seem that such flashy dwellings would leave this animal prone to predation, the opposite is true. 

Butterfly pupae are easy targets: defenceless protein sausages that are too busy scrambling and rearranging their insides to fend off would-be predators. It forces them to conceal their identities in order to survive this dangerous life stage – and polymnia relies on light-bending to do the trick.

"They are actually very hard to see in nature, given the way all the colours are reflected," explains Dr Keith Willmott, one of the world's leading tropical butterfly experts.

The tactic works a charm, and is actually shared by species in several other groups, like milkweed butterflies (genus Danaidae) and those in the genus Tithorea.

Moustached men? It's hard to un-see the grumpy faces in these Tithorea pupae. Image: Deus Mortus/used with permission 

Contrary to some comments online, these structures don't contain metal particles; they're made of chitin, the same substance that gives insects like jewel beetles their shine and turns the sea mouse into a rainbow-coloured, fibre-optic lamp. 

But that's not the only fallacy about these animals floating around the web. A quick Google search will tell you that the empty chrysalises were once used as currency. It's tempting to conjure up the scenario: baskets filled to the brim with sparkling caterpillar cases and ancient peoples combing the undergrowth for the rainforest's doubloons. We humans certainly love our shiny things, but after speaking with half a dozen butterfly specialists, it looks like there's no truth to this historical nugget.

For starters, empty (or "dead") pupae are extremely fragile, so the idea that they would hold up long enough for currency exchange is farfetched. And there's another problem, too.

"The butterflies are only in the pupal stage for around a week, depending on the species," explains Dr Ryan Hill, who reared Mechanitis butterflies for his research in Ecuador. "Afterward, they lose the metallic colour."

Just three days separate this photo, and the one at the beginning of this article. The chrysalis begins to dull even before the butterfly within is ready to emerge. Image: Rubens Luciano/used with permission
Adult tiger clear wing. Image: Rubens Luciano/used with permission

Costa Rica native Luis Ricardo Murillo-Hiller, who has been studying butterflies and working with butterfly farmers for 25 years, agrees. "They lose their metallic colour almost immediately," he says. "I have never seen or heard of somebody, in any place, using the pupae as currency, and actually, they are almost to unknown to [the average person]."

These pupae aren't very abundant, so unless you're out searching – and we mean really rooting around – in the local flora, chances are you'll never find one.

That's one myth busted – but our dig into internet lore did reveal that there is a lot we don't know about metallic camouflage. Some speculate that being shiny has other protective benefits too.

It's possible that the reflective properties of their chrysalises mask the butterfly larvae by making them look like something else entirely: hanging drops of water, shafts of light, empty pupae, or dry, curled leaves.

Image: melanie cook/Flickr

"The empty pupa idea is pretty cool," says Hill. "There are studies on seed colouration showing that when seeds are mottled they resemble empty seeds, and so are passed up by [seed-eating animals]. I would love to do a study on this in insects!" 

For hungry animals that get too close, the mirror effect might also be enough scare them off. Birds, lizards and other visual hunters like jumping spiders scour native plants for prey, and reflected movement (or the sudden appearance of their own reflected form) would likely initiate a bail sequence. 

These caterpillar contractors are among countless examples of the incredible biodiversity the rainforest has to offer. And yet over 750,000 square kilometres (289,000 square miles) of this vital habitat have been destroyed since the late 1970s.

Costa Rica has made encouraging strides to combat deforestation. In 1996 the country issued a complete ban on razing mature forest, and in the years since we’ve seen significant growth. Half of the remaining rainforest is now protected under national parks and biological reserves – but even here, just a quarter of the original tree cover is still standing and agricultural expansion continues to threaten what's left. If we want to unravel the rainforest’s many secrets, we should be doing much more to protect it.



Top header image: Kristi/Flickr