Plastics are incredible. They are one of the most fascinating and useful inventions of the modern world. The keys I am pressing right now to type these words are made of plastic, the pen I used to take the notes for this piece was made mostly of plastic, heck, you may even be holding a piece of plastic in your hand right now in order to read this article. We just can’t get enough of it. According to the New York Times, as much as 300 million tons of plastic is produced globally each year, with less than 10% of it being properly recycled.

This creates a problem on a truly staggering scale. What do we do with all of that plastic once we’re done with it? The long-lasting durability of plastic is a great feature when we’re making use of it, but once it is discarded, this longevity means our waste will be sitting around for hundreds or possibly even thousands of years, filling up landfills and polluting our environment.

Now a group of Spanish researchers have turned their attentions to a tiny caterpillar with an unusual ability: digesting polyethylene plastic.



Eating the Least Nutritious Part of Your Garbage

If you take a look at the contents of an average household’s garbage can, most of what you find can be food for creatures a little lower on the food chain. Discarded food stuffs might be big enough to feed scavengers, or ideal for molds, fungi, and bacteria to work their decomposing magic upon. Even cardboard, wood, and biodegradable plastics can be broken down by hard-working microbes. Rust can even eat away at seemingly invulnerable metals. Generally speaking, plastics stick out in our garbage bins as being by far the least nutritious and most undesirable part of the whole mess. Plastic, it seems, has no place in the food chain.

This line of thinking is why a researcher for the Spanish National Research Council (CSIC), Federica Bertocchini, was so surprised when she discovered tiny caterpillars eating through a polyethylene plastic bag she had placed them in. The discovery came serendipitously one day when Bertocchini, an amateur beekeper, found her hives being invaded by a scourge of caterpillars, as reported by this article from ResearchGate.

These little caterpillars, also sometimes called by the common name “waxworms,” are the larval stage of the Greater Wax Moth Galleria mellonella. A very common moth found across Eurasia, North America, and Australia, Galleria mellonella caterpillars are sometimes sold as food in pet stores for reptiles. They also sometimes make a pest of themselves thanks to their fondness for feasting on the honeycomb inside of beehives, where they earn their nickname the waxworm for their peculiar habit of eating beeswax.

After removing a number of the caterpillars from her beehives, Bertocchini returned later to find holes in the plastic shopping bag where she had collected the caterpillars. They had chewed their way to freedom, leaving Bertocchini with an intriguing mystery.

Digesting Plastic

When Bertocchini noticed the holes in her bag, she was immediately curious about where the plastic had made its way to. If the caterpillars had simply chewed their way to freedom it would not be much of a story, but if they had actually eaten and digested the polyethylene plastic, that would be altogether remarkable.

Evaluating the caterpillars in the lab showed that, remarkably, they were actually digesting the plastic. Given little films of polyethylene plastic, like the type you’d find in a shopping bag or disposable food container, the caterpillars began producing holes in the film within 45 minutes. Researcher’s observed the caterpillar’s digesting the polyethylene into a compound called ethylene glycol, a biodegradable compound used in manufacturing.

Publishing their findings in Cell with a paper entitled “Polyethylene bio-degradation by caterpillars of the wax moth Galleria mellonella,” the researcher’s speculate that the source of the waxworm’s unusual ability to digest plastic may have originated with its ability to digest beeswax, which has some chemical similarities to polyethylene. However, they also note that this ability may not be entirely the caterpillar’s invention, suggesting the bacteria in its digestive system might be the source of this chemistry: “[i]t is not clear whether the hydrocarbon-digesting activity of G. mellonella derives from the organism itself, or from enzymatic activities of its intestinal flora.”

Putting the Worms to Work

This discovery might conjure up the image of plastic-hungry caterpillars devouring their way through our landfills as they help alleviate one of our trickiest global waste problems. But the reality is that we don’t need to worry about a plague of caterpillars growing fat on our plastics. If waxworms or the Greater Wax Moth had any real taste for plastic, we would have encountered a serious problem long ago. Widely distributed across the globe, the waxworm would be well-positioned to cause some serious havoc if it suddenly developed a craving for plastic.

Since we don’t hear of waxworms devouring lawn chairs or eating up the plastic in our garbage, they don’t seem too interested in dining on plastic. Even when they ate through Bertocchini’s bag they didn’t stick around for a snack. They simply ate their way to freedom and crawled off to find a more nutritious meal. On the whole, this is probably a good thing for anyone who likes their plastic possessions. But it’s not such a good thing for putting these worms to work.

Bertocchini et. al. observed the caterpillars to be consuming a pretty minuscule amount of plastic. Placing approximately 100 of the caterpillars in a standard grocery store polyethylene plastic shopping bag, the researcher’s observed the caterpillars to have eaten about 92 milligrams of the bag after 12 hours. For some perspective, a plastic shopping bag weighs around 5.5 grams.

So within 12 hours, those ~100 worms ate just 1.67% of that single plastic shopping bag. It would take them a whopping 717 hours, just shy of 30 full days, to consume an entire plastic shopping bag. A month is certainly an improvement over scientist’s estimates that a plastic shopping bag might take as much as 20-1,000 years to decompose in the environment, a process which only breaks it down into microscopic particles, not actually converting it into something else. Still, it would take far too long, and require far too many waxworms to make putting them to work practical. But the story doesn’t stop there…

The Wonders of Chemistry

While the caterpillars themselves might not be the agents of plastic removal we so desperately need, the chemistry secrets at work in their guts might hold the answers we’ve been looking for. “There is the possibility that one molecule could [degrade polyetyhlene,] so the idea would be to isolate it and reproduce it at a large scale, and use this to degrade the plastic waste,” (sic) said Bertocchini in the ResearchGate article linked above.

This is an amazing idea. Instead of putting any sort of life form – be it microbes, worms, caterpillars, or whatever – to work eating up our garbage, the way to tackle the plastic waste problem might come from the chemist’s laboratory. With a compound like Bertocchini is describing, we might be heading towards a future where some type of chemical can be sprayed onto our landfills to encourage plastic degradation. If a single chemical capable of degrading polyethylene into ehtylene glycol can be isolated from the waxworm’s gut, the forecast for getting rid of the plastics in our landfill could be reduced from millennia to months.

The Bacterial Approach

As it turns out, while the recent CSIC study from Bertocchini and her colleagues is attracting headlines and attention, CSIC was not the first to identify the potential of the waxworm, nor the first to study it. Chinese researchers from Beihang University published a study in 2014 entitled “Evidence of Polyethylene Biodegradation by Bacterial Strains from the Guts of Plastic-Eating Waxworms”.

Although somewhat different from the Galleria mellonella caterpillars studied by Bertocchini, the Plodia interpunctella (Indian mealmoth) caterpillars which are the focus of this study are also referred to as “waxworms” and are very similar to G. mellonella. Both species have been observed eating polyethylene plastic. In the study, the researcher’s isolated two strains of bacteria, Enterobacter asburiae and Bacillus sp., from the gut of Plodia interpunctella caterpillars and demonstrated that both of these bacterial strains are capable of growing on a polyetyhlene plastic film. Over a 28-day period, the researcher’s observed biofilms forming on the plastic as the bacteria grew, and scarring on the film likely resulting from the bacteria digesting the plastic.

This amazing result gives strong evidence to the theory that the source of the waxworm’s ability to digest plastic comes from its gut bacteria. This opens up the potential for utilizing the bacteria themselves to do the work of tackling our plastic problem. Properly cultivated and released in controlled environments, these bacteria could be utilized to finally make waste plastics biodegradable at the end of their useful lifetime.

More Questions Than Answers

Like with any good discovery, the knowledge of this amazing plastic-metabolizing activity in the waxworm’s gut leaves us with far more questions than it does answers. While research efforts like those at CSIC or Beihang University begin to unravel just how to best make use of these developments, we are left with some rather entertaining science fiction daydreams as to some of the more spectacular and catastrophic effects something like a bacteria – or a worm – that can eat through the world’s plastic supply might have.

Although figuring out how to best put this discovery to use may still a long way off these findings have forced many to reconsider how they look at polyethylene plastics. Classically considered non-biodegradable, PE plastic has met its match in the waxworms and their gut bacteria which demonstrate to us once again that, indeed, life finds a way. Knowing that it is possible is half the battle, and with this knowledge scientists may have an opportunity to rethink waste management.

A Few Words About Polyethylene

It is very important to point out that throughout this article and in the studies we’ve looked into, the focus has been on digesting a specific type of plastic called polyethylene. Although polyetyhlene is the most common type of plastic, it is far from the only type of plastic. Polyetyhlene (PE) is often found in two forms, Low Density Polyethylene (LDPE), and High Density Polyethylene (HDPE) – both of which are commonly used for the types of plastic shopping bags we talked about above.

Probably the type of disposable plastic we’ve focused the most on here at Hydration Anywhere is also a sort of polyetyhlene, known as Polyethylene terephthalate or PET. PET is the type of plastic most commonly used for disposable water bottles, which frequent readers of Hydration Anywhere will know we’ve spent a lot of energy fighting against.

Unfortunately, PET plastic has some differences from the types of polyethylene the waxworms are capable of digesting. None of the studies we could find give any mention of testing the waxworms on PET plastics, so while it is possible they can digest them as well, we have no evidence to suggest that they can.

But as it turns out, the waxworms’ may already be performing the real heavy lifting. In an online discussion, a reddit user verified as a PhD in Organic Chemistry on the /r/science subreddit, known as ECatPlay, offered some illuminating information. To quote Dr. ECatPlay (source):

“The thing about polyethylene, is that it doesn’t have any convenient functional groups, or weak links that an enzyme can attack. PET (polyethylene terephthalate) has ester linkages. These are fairly stable, but can be hydrolyzed with acid or base. So being able to degrade PE is especially challenging.”

Something To Look Forward To?

While an army of worms might not be the solution to our global plastic problem, the proof lurking in their gut that Mother Nature is capable of engineering a solution to our plastic plague is certainly a reassuring one. With any luck, this will be a development worth following into the future and something that will pop-up in the headlines as new developments arise.

Discoveries like this offer scientist’s a vast frontier to explore as they plumb the depths of nature’s mysteries for novel solutions to our most pressing problems. We salute the efforts of these scientists and researchers and look forward to covering them more in the future.

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We explore new research which demonstrates that plastics traditionally thought of as non-biodegradable might not be so tough when faced with the common waxworm.