Skulls have been used for centuries by humans in spooky scenarios and as frightening symbols to signal danger. It turns out that a caterpillar species, the rubber leaf skeleton, does the same in the insect world.
This macabre little animal stacks skulls on its head to repel predators.
These gothic, 25 mm long creatures “really capture the imagination,” says Dieter Hochuli from the School of Life and Environmental Sciences at the University of Sydney, Australia. They live in the eucalyptus forests of Australia and New Zealand and have probably been around for millions of years. “Insects do a lot of strange things, but these guys look really strange,” Hochuli told Tekk.tv.
Like many other creatures, they must moult or shed their skin if rubber leaf skeletons are to grow. In this caterpillar species, their head is part of their skin. Normally the creatures would just throw everything away, “but these guys create a tower of five, six or seven heads up there,” says Hochuli, “and they use them to scare off things that try to eat them.
Hochuli’s university faculty began working with these fascinating creatures for the first time in 2012, before behavioral ecologist Petah Low published a study on the skeletonizer in 2014.
Previously the rubber leaf skeletonizers were called from the unicorn caterpillar to the crazy Hatterpillar and are scientifically known as Uraba lugens. Each caterpillar moults about a dozen times before it turns into a cocoon and becomes a moth – but first they must avoid attack.
Not only do they look threatening, these clever creatures also use their Halloween-like headgear as bait. Ideally, the predators take a chip from the old block instead of the caterpillar.
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A rubber leaf skeleton shows his threatening representation of skulls
Professor Dieter Hochuli/School for Life and Environmental Sciences, University of Sydney
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A rubber leaf skeleton shows his threatening representation of skulls
Professor Dieter Hochuli/School for Life and Environmental Sciences, University of Sydney
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A stink bug attacks a rubber leaf skeletonizer, but manages to hit its skull cap.
Professor Dieter Hochuli/School for Life and Environmental Sciences, University of Sydney
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A group of rubber leaf skeletons on a eucalyptus leaf
Professor Dieter Hochuli/School for Life and Environmental Sciences, University of Sydney
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A group of rubber leaf skeletons with skull hats
Professor Dieter Hochuli/School for Life and Environmental Sciences, University of Sydney
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Do not mess with me! A rubber leaf skeletonizer with his bizarre headgear skull stack
Professor Dieter Hochuli/School for Life and Environmental Sciences, University of Sydney
One such predator is the stink beetle, an insect to whose mouth is attached a huge needle filled with toxins. “They feed by injecting the needle directly into their prey. We have videos of them trying to attack these caterpillars, and the first thing the caterpillar does is to wave its head around and push them away, so to speak,” Hochuli said.
“We have also seen how the beetle tries to drive the needle into the caterpillar, and what it does is to hit the empty head pieces so that the caterpillar can escape.
Until the predator figured out what was going on and that it actually speared a skull instead of a juicy caterpillar, the caterpillar hopefully had a chance to escape and leave its old skulls behind at the scene.
“Carrying heads in this way is a real advantage for the caterpillar,” says Hochuli. “Many people think it’s a pretty metallic way to live their lives.
If the caterpillar escapes, there is a chance that one of the other caterpillars in the group will be shot instead.
“These caterpillars are sociable, they tend to eat in groups lined up in tufts, and we’re pretty sure that carrying skulls is not only to avoid being eaten, but also to get the predator to focus on the guy next to you. It distracts long enough for the predator to turn around and say, ‘I’m going to eat this one instead,’ says Hochuli.
“You are an animal that reacts really quickly to a change in environmental conditions, they always find a way to survive.
“With evolution, the selection pressure not to be eaten is massive – so if you can gain an advantage that allows you to go through life, you take it. This is certainly one of the best ways to avoid being eaten, along with super-toxic, color-preserving, and colorful, colorful, and colorless foods.
