Jewel caterpillars at the nudibranchs of the forest
Images: Daniel Janzen and artour_a at Flickr

Jewel caterpillars belong to the Dalceridae family of moths, of which there are 84 species found all over North and South America. Sometimes referred to as ‘slug caterpillars’, because of their fat bodies and gooey appearance, the larvae of these moths are some of the most striking insects you’ll see anywhere in the world.

Ferris Jabr has a really great run-down of these creatures at Scientific American, and says that while bright colours and patterns in nature usually mean, “back off, I’m poisonous”, in jewel caterpillars, the purpose is not immediately clear. Biologist Daniel Janzen from the University of Pennsylvania in the US raised a number of Dalceridae caterpillars in his lab to try and figure out the purpose of their colours, and found that despite the fact that they spent a lot of time crawling out in the open, seemingly unafraid of predators, he couldn't find any evidence of toxins or a sting. 

What biologists do know, says Jabr, is why jewel caterpillars of the Dalceridae family have glutinous gumdrop spines. They break off so easily that their function could be similar to that of a lizard’s tail, the way it snaps off and distracts a predator while the rest of the lizard shuffles off to safety. 

And it helps that the caterpillars’s gumdrop spines are sticky, because if anyone gets a mouthful, they’re going to be more concerned about cleaning their mouths out than they are about pursuing the creature for more goo.

Fabr explains at Scientific American:

"In one telling experiment, Marc Epstein - an insect biosystematist at the California Department of Food & Agriculture - and his colleagues placed Dalcerides ingenita larvae in glass Petri dishes and introduced a few ants (Camponotus floridanus) to each dish. Many ant species devour caterpillars and other plump grub if they get the chance. 

Once inside the Petri dish, the ants inspected the larvae with their antennae, but most backed off without trying to take a bite. The few ants that chomped down got their mouths temporarily stuck in the larvae’s jelly coat or pulled away quickly and cleaned the gunk off their mandibles."

Head to Fabr’s article at Scientific American for more information and images of these incredible insects, and here's a video of a little jewel caterpillar making its way across some screwdrivers: