Caterpillar 'Plastivores' Can Eat and Digest Plastic Bags

Each year, human beings produce about 400 million metric tons of plastic, a number that's set to double in the next 20 years if oil and gas companies succeed in opening new plastics plants. That's despite a burgeoning plastic pollution problem and, in reaction, plastic bans in many communities.

A way to safely dispose of plastic would be welcome, if only to deal with the plastic we've already created. One solution might be in micro-organisms and insects. A group of around 50 organisms, ranging from bacteria and fungi to bugs — about 50 species in all — are plastivores, meaning they can eat and digest plastic.

The research into what plastivores can eat (and how it may or many not damage the organisms, and what kind of waste they excrete) has been going on for the last few years.

One of the insects already identified as a plastic-eater is the wax moth. The wax moth and its larvae (caterpillars) are known to invade beehives to eat the honeycombs inside. That the wax moths might be able to eat plastic, too, was anecdotally known. In 2017, a scientist who was also a beekeeper, Federica Bertocchini at the Institute of Biomedicine and Biotechnology in Cantabria, Spain, tested this. She found that the wax moth caterpillars broke the plastic down quickly while eating it.

But what wasn't understood was how the caterpillars actually digested the plastic, only that they did it somehow. So a group of researchers from Brandon University in Manitoba, Canada, set out to further study the wax-moth caterpillars (aka waxworms). Their research was recently published in the biology journal, Proceedings of the Royal Academy B.

"The waxworm and its gut bacteria must break down these long chains (in honeycomb)," the study's lead author, Christophe LeMoine, told Discover magazine. "And presumably, because plastics are similar in structure, they can also co-opt this machinery to use polyethylene plastics as a nutrient source."

Feeding them only polyethylene bags — the type of plastic most grocery bags are made from, and a common waterway and beach pollutant — the scientists found that 60 caterpillars could eat 30 square centimeters of plastic a week, and importantly, they could survive eating only the plastic.

No, the waxworms weren't just breaking the plastic into smaller pieces and pooping it out. The researchers found that the gut microbiomes of the caterpillars contained bacteria that were breaking down the plastic. The downside? The caterpillar poop contained ethylene glycol, a toxin.

"Nature is providing us with a great starting point to model how to effectively biodegrade plastic," said LeMoine. "But we still have a few more puzzles to solve before using this technology, so it's probably best to keep reducing plastic waste while this gets figured out."