There is nothing I love more than finding an amazing new insect to tell you about! Today it’s the “Mad Hatterpillar.” As you can see from this photo, these caterpillars (Uraba lugens, larvae of a Gum Leaf Skeletoniser moth) have a strange attachment to their heads. It’s a stack of their shed head capsules! These caterpillars are native to Australia and eat eucalyptus trees.
Where do they get all these extra heads, anyway?
Moths and butterflies are just flying gonads that make new caterpillars. Caterpillars are feeding machines with one primary purpose: eating enough food to build the body of a future moth or butterfly. A caterpillar stuffs itself with food, but eventually is limited by its exoskeleton, which is rigid and can’t grow. ‘Pillars deal with this by splitting their external skin, shedding it, and making a new, bigger exoskeleton so they have room to grow. For some reason, this species of moth caterpillars keeps their heads and build themselves a strange “hat” that gets taller as they grow.
Why do they build themselves a hat? Are they headed to Ascot? A royal wedding? No one really seems to know WHY the caterpillars keep their old heads hanging around. From a 1980 paper describing the biology of the caterpillars:
“It is hard to imagine what, if any, purpose the retention of a stack of head capsules might serve. Perhaps it might attract the first one or two investigative pecks from a bird or lizard; the predator would initially obtain only a mouthful of dry exuviae [BG note: exuviae =shed skins]. However, the dense, hairy coat alone would probably serve as an adequate repellent for most birds. If a bird really desired to consume one of these larvae, it is unlikely that it would be deterred by a stack of rather easily-dislodged exuviae attached to one end of the morsel.”
If you do happen to see one of these, you should not touch it! Apparently these caterpillars are covered with highly itchy and irritating spines–which seems to make their chapeau of old heads a bit redundant.
Most newer publications about this insect focus on its status as a pest of Eucalyptus, rather than it’s strange headgear. Clearly this is a thesis in search of a graduate student!
By the way, some related Nolid moth caterpillars have balloon heads, which is freaky in an entirely different and wonderful way.
McFarland, N. (1980). Retention of cast head capsules by some nolid immatures in four Old World countries. Journal of Research on the Lepidoptera., 17 (4).
Thanks very much to nuytsia_pix for letting me repost these photos!