Meet 'Mad Hatterpillar,' the caterpillar that uses its old heads for defense

(CNN)In the dense eucalyptus forests of Australia, deadheads forage leaves and wriggle their bodies around. No, these aren't Grateful Dead fanatics stranded since the psychedelic shows of the 1970s.

Native to Australia, Uraba lugens is a strange caterpillar that stacks its molted heads atop each other. With every molt, the stack becomes an increasingly tall, tapering tower since every head is larger than the last.
Uraba lugens' headpiece can stack up to 12 millimeters tall — nearly half its maximum body length of 25 millimeters.
That's how this freaky creepy-crawly got its nickname, the "mad hatterpillar." This morbid headgear serves as a diversion when hungry predators are about.

    The metamorphosis

      Like all insects, these caterpillars go through stages during which they shed their outer skin, including their heads. Depending on the quality of the food available to them, U. lugens go through eight to 13 larval stages, or instars, on their way to becoming pupae, said Dieter Hochuli, a professor of school of life and environmental sciences at The University of Sydney in Australia. That's the stage during which the larvae, within their cocoons, transform into adult moths.
        Other caterpillars would normally shed their skin and heads and leave them behind. But U. lugens, and a few other species of caterpillars, just can't let go of its molted baggage.
        "The molted head capsules start stacking early but they are not always visible, as the smaller ones get dislodged over time," Hochuli said. "It's not uncommon to see caterpillars with at least five old heads stacked on top of the one they are currently using."
          For weeks before they become moths, these insects carry their dead heads, which can stack up to 12 millimeters (0.47 inches) tall — nearly half of the caterpillar's maximum body length of 25 millimeters.

          A peculiar method for defense

          The primary reason for the caterpillars' head-stacking behavior is, reportedly, to keep from being eaten.
          "They look bigger, so they're more threatening and look more formidable to a potential predator," said Alan Henderson, wildlife manager of Minibeast Wildlife, an invertebrate education and resource center in Queensland, Australia. "Another theory is that it may provide a false target, so a predator such as a jumping spider or something that's targeting a part of the animal might go for the wrong part. It gives the caterpillar a chance to get away."
          U. lugens also use their heads as a weapon or shield against various insects, especially repelling assassin bugs that try to inject the caterpillars with a needle-like mouth and suck out their insides.
          Eaten water beetles stay alive by escaping through the predator's anus