The Plastic-Eating Caterpillar: A New Clue in the Quest for Biodegradable Plastic?

 

A novel possibility for cleaning up the earth’s rising tide of plastic waste was reported this week in the form of a newly discovered, plastic-eating caterpillar.

 

The Problem with Plastics

 

Ubiquitous, essential to modern life, produced in exponentially increasing quantities, and persisting forever: plastics are taking an increasing toll on the planet. We produce around 300 million tons of the synthetic polymer every year, the majority of which ends up clogging landfills and polluting the environment. Millions of tons of plastic makes its way into the ocean annually, with catastrophic consequences. The problem: plastic does not degrade, it just accumulates.

 

An Insect-based Solution?

 

Now, researchers in Spain have discovered that a caterpillar known as the wax worm can digest polyethylene. Led by Dr. Federica Bertocchini, of the Spanish National Research Council, the scientists found that this caterpillar can eat its way through plastic bags quite effectively.

 

Small and plump-bodied, the cream-colored wax worm is the larval (caterpillar) stage of the common wax moth (Galleria mellonella), also known as the honeycomb moth. This tiny moth is a big problem for beekeepers because it lays its eggs inside beehives. After hatching, the larvae – wax worms – feed voraciously on honeycomb.

 

Discovery of the plastic-eating prowess of the wax worms began with a small piece of serendipity connected to Bertocchini’s hobby: bee keeping. After noticing a moth infestation in her beehive, she collected the larvae responsible and held them in a plastic bag overnight, only to find that they chewed holes through the bag to escape. Amazed and intrigued, Bertocchini and colleagues decided to investigate further.

 

Polyethylene Polymers

 

Plastic bags are made from polyethylene, the most common form of plastic.

 

Polyethylene is:

 

  • Comprised of long chains or polymers of carbon atoms.
  • Extremely persistent in the environment.
  • Almost totally resistant to breakdown by normal composting microorganisms.

Beeswax is likewise a long polymer involving single carbon-to-carbon bonds, in some ways like a natural plastic, according to Bertocchini, with some structural similarity to polyethylene. This raised a question: might worms that chow down on beeswax for a living also possess a previously-unimagined ability to break down plastic?

 

Uncertain at first whether the holes she found were just mechanical chewing or evidence of real digestion, Bertocchini turned to lab studies to see what the caterpillars could do when presented with a pile of plastic. The results demonstrated actual digestion, confirmed by the detection of a breakdown product, ethylene glycol, inside the feasting caterpillars.

 

It is uncertain whether the caterpillars themselves possess the enzymes to break down the polyethylene bonds, or whether they have cultivated a microbiome of gut bacteria able to do the job for them, but either way, the discovery is momentous.

 

Practical Implications

 

In the lab study, it took 100 worms twelve hours to eat only 92 milligrams of plastics, a relatively tiny amount on a global scale. However, given that virtually no biological breakdown mechanism was previously known, even slow munching by some worms is an event causing much excitement.

 

Researchers are excited about the larger implications. Follow-up studies will examine the molecular basis of the polyethylene-digesting ability of wax worms and their gut bacteria. This work holds intriguing possibility for opening a door to better bio-disposal of plastics in the future.

 

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