Insects that can eat and digest plastics

At first glance, there is nothing particularly remarkable about these worms.

The larval form of the moth mellonella gallery, also known as honeycomb moth or wax moth, it feeds on the wax that bees use to make their honeycomb. For beekeepers, they are pests that they try to get rid of quickly, without thinking twice.

But in 2017, molecular biologist Federica Bertocchini, who at the time was researching the embryonic development of vertebrates at the Spanish National Research Council, found herself faced with a potentially environmentally revolutionary discovery involving these creatures.

An amateur beekeeper, Bertocchini came across these larvae by chance, when she was cleaning her hive.

“I put the worms in a plastic bag and, before long, I noticed that they were making holes (in the plastic),” she says in an interview with BBC Earth.

There was something that caused the plastic to degrade when it came into contact with their mouths.

“It was a real eureka moment — it was incredible,” remembers Bertocchini, referring to the initial discovery and the notion of what it meant.

“It was the beginning of the story. The beginning of the research project, of everything.”

The larvae were doing something that we as humans find extremely difficult to do: breaking down plastic, which takes several decades to centuries to completely break down.

Bertocchini and his fellow researchers began collecting the liquid excreted from the larvae’s mouths. They discovered that this “saliva” contained two crucial enzymes, called Ceres and Demeter — named after the Roman and Greek goddesses of agriculture, respectively — that were capable of oxidizing the polyethylene in the plastic, essentially breaking down the material upon contact with it. .

“It takes a few hours, at room temperature, in an aqueous solution,” she explains.

Furthermore, the larvae appeared to be digesting the plastic as if it were food.

“When the worm eats the plastic and starts to break it down, its intestine reacts practically as if it were eating normal food. This means that there is something going on with the animal’s physiology that extracts something from this plastic biodegradation. And it just continues, as if it were a normal diet,” Christophe LeMoine, professor of comparative physiology at Brandon University in Canada, tells BBC Earth.

Inspired by Bertocchini’s discoveries, he also began to study these larvae.

“We discovered that the plastic allowed them to retain all the fat and, presumably, continue with their life cycle”, he adds.

Basically, these larvae are eating everything in sight, before turning into moths, at which point they no longer eat, they just reproduce.

“I always call them flying gonads, because that’s all they do,” jokes LeMoine.

Leaving these worms loose in an environment polluted by plastic can be dangerous for ecosystems, especially given their ability to destroy bee hives, as Bertocchini notes. But she is hopeful that the enzymes these larvae produce could in the future help combat plastic pollution worldwide.

There is, therefore, a race underway to discover how this mechanism works.

“That’s the million-dollar or trillion-dollar question, because once we figure that out, we’re going to be able to break down a trillion dollars of plastic,” says LeMoine.

Bertocchini is now chief technology officer at bioresearch startup Plasticentropy France — she works with a team to study the feasibility of applying these enzymes for widespread use in breaking down plastic.

“The main objective is to be able to apply these enzymes to plastic waste,” explains Bertocchini.

“I really want this discovery and technology to be developed and turned into a solution that we can use globally.”

But, after all, why is plastic so difficult to decompose?

In nature, most things decompose because decomposer organisms break the chemical bonds that hold a substance together.

They have evolved over millennia to decompose everything they come across. Until plastic came along — which, despite its current bad reputation, conquered the world.

Plastics are made up of long chains of polymers with very strong bonds. And one of the secrets to breaking these bonds is oxidation.

This is what the larvae appear to be doing with their saliva, introducing oxygen molecules into the plastic.

“And this is sometimes achieved in the environment through light, for example, high temperature. And this is the bottleneck. It takes a while because the environment has its own time”, explains Bertocchini.

“So what the larvae do is simply introduce an oxygen molecule. And, in a few hours, instead of months or years, or however long it is. It’s a way to solve the bottleneck of this reaction.”

Promising enzymes for this purpose can be found in several different organisms. In fact, more than 30,000 enzymes have already been identified, capable of digesting 10 different types of plastics.

Some fungi and bacteria are known to digest plastics, but this is much rarer in complex animals. In 2022, it was discovered that another invertebrate also likes plastic – the “superworm” Zophobas moriowho can gain weight on a polystyrene diet.

A bacteria found in the stomach of cows can be used to digest polyester.

But one that is generating a lot of interest from researchers is a bacterium called Ideonella sakaiensisand above all its PETase enzyme.

PET plastic, most common in plastic bottles, takes hundreds of years to decompose in the environment. But PETase is able to break it down in a matter of days.

Currently, 400 million tons of plastic waste are produced globally every year.

Of this total, 19 to 23 million tons (the equivalent of around 2 thousand trucks of garbage) infiltrate aquatic ecosystems, where much of it is colonized by microorganisms or eaten by animals.

A series of global measures will be needed to reduce our dependence on and consumption of plastic. To this end, many countries have committed to helping reduce the production and use of single-use plastics, and a global plastics treaty is expected by the end of 2024.

But if enzymes like these can someday be mass-produced to break down plastic, the little creatures that munched on Bertocchini’s bag could perhaps play an important role in that too.