Very hungry caterpillars

It’s almost a pity that we introduce children to caterpillars so young. The magic of the transformation of a squishy, unimpressive tube into a living, fluttering creature apparently made of stained glass gets muddled up with the rest of the magic of childhood and is too easy to forget when we grow up. Everyone knows about caterpillars turning into butterflies, but almost no one really thinks about it.

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Photo by Andrea Westmoreland, reproduced through a Creative Common license from Flickr.

Even before they turning into butterflies (or moths), caterpillars are impressive. They hatch tiny, into a bird-eat-caterpillar world, and their one crucial job is to grow big in time to metamorphose. This isn’t a particularly complex task—there’s a reason caterpillars are basically just digestive systems on legs—but it isn’t necessarily easy, either. They need to find the right food and eat it quickly without being eaten themselves.

When you imagine caterpillar food, what comes to mind? Plants, naturally. You may have heard that some caterpillars can eat toxic plants and sequester those toxins inside their bodies, protecting themselves with the poison that was meant to protect against them.

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Monarch caterpillar, which feeds on the toxic milkweed. Photo by Ben Saren, reproduced through a Creative Common license from Flickr.

Some caterpillars have much more gourmet tastes. Caterpillars in the genus Ceratophaga specialize on keratin: they eat the horns and hooves of dead animals. Imagine trying to eat a hoof—imagine trying to grow big by only eating a hoof. Keratin is technically protein, but it is not easy to digest; the caterpillars have to use specialized enzymes to do so. One species, Ceratophaga vicinella, not only specializes on keratin: it specializes on only the keratin in the shells of dead gopher tortoises. This little caterpillar (which grows up to be a little moth) is found in Florida, and depends entirely on gopher tortoises dying so that it can build a little silk tube on the shell and munch away. To be clear, the caterpillars don’t attack living tortoises: they just recycle them after they’re gone. Gopher tortoises themselves are on the decline, so this strange little caterpillar is probably in trouble, too.

Another enterprising caterpillar, Galleria mellonella, misleadingly dubbed the wax worm (not a worm!), specializes on beeswax. Beeswax is another substance that, while technically containing energy, is not the first or the fifth or the twentieth thing you might choose to subsist on. But nature likes to fill an unexploited niche, and before the wax moths, no moths were laying their eggs in beehives—so the wax moth went for it.

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Adult wax moth on a beehive, presumably laying eggs. Photo by Maja Dumat, reproduced through a Creative Common license from Flickr.

If you aren’t impressed yet, hang on—you will be. Researchers took wax worms and put them on plastic bags. You know those thin, awful plastic bags that every store gives you, that are always blowing out of trash cans and getting stuck on trees and choking sea turtles? They put the wax worms on those bags.

Now, everyone knows plastic isn’t biodegradable. It is made from oil, which is technically a biologically-derived product, but you can bury plastic in the ground and it will just sit there. Scientists speculate that future paleontologists will be able to identify the start of our modern era by the layers of plastic in the ground: they’ll dig, and the rock layers will be, in order from bottom to top, dinosaur fossils—giant sloth fossils—woolly mammoth fossils—thick layer of plastic bags.

But those wax worms that usually eat beeswax—they ate the plastic bags. Not quickly, but they did it. Just think what it would mean if we had a way to break down plastic: we could tackle that underground layer of garbage, and those floating garbage islands in the oceans too. Maybe the humble, hungry caterpillar will help us undo some of the environmental damage we have done.

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Save us, little buddy! Photo by nick goodrum, reproduced through a Creative Common license from Flickr.

References

Bombelli P, Howe CJ, Bertocchini F. 2017. Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonellaCurrent Biology 27:R292-293.

Deyrup M, Deyrup ND, Eisner M, Eisner T. 2005. A caterpillar that eats tortoise shells. American Entomologist 51(4):245-248.

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