In Eric Carle’s 1969 children’s classic The Very Hungry Caterpillar, the title character eats plums, apples, strawberries and organs – but not, funnily enough, plastic shopping bags.
If the book were ever to be updated for modern audiences, that’s a little plot detail ripe for revision.
Researchers at the Institute of Biomedicine and Biotechnology of Cantabria, in Spain, have discovered at least two species of caterpillar are able to digest polyethylene bags – the ubiquitous carriers used by supermarket shoppers – offering a potential strategy for tackling a major component of landfill around the world.
The scientists, led by Federica Bertocchini, report their findings in the journal Current Biology.
The initial discovery was made by happy accident, when Bertocchini noticed plastic bags containing the caterpillars of the honeycomb moth (Galleria mellonella) developed holes after just a few hours.
Investigating the discovery, Bertocchini’s team realised the caterpillars weren’t just biting through the plastic; they were digesting it and converting it into ethylene glycol – a colourless, odourless liquid used on an industrial scale in the manufacture of polyester fabrics and antifreeze.
Though moderately toxic to humans, ethylene glycol is far less harmful to the planet than the polyethylene from which it is derived.
The scientists do not yet know the precise mechanisms by which the moth larvae break down the plastic but strongly suspect it is the result of adaptations that evolved to allow the species to occupy their particular ecological niche.
Honeycomb moths lay their eggs inside bees’ nests, and newly hatched caterpillars feast on beeswax.
“Wax is a polymer, a sort of ‘natural plastic’, and has a chemical structure not dissimilar to polyethylene,” Bertocchini says.
Converting beeswax and polyethylene into food might involve breaking down similar chemical bonds, the researchers suggest.
The discovery of the honeycomb moths’ predilection for plastic follows a 2014 Chinese study that found the same abilities in the caterpillars of the Indian mealmoth (Plodia interpunctella) – also a beehive dweller.
The earlier work, led by Jun Yang of Beihang University, Beijing, found the larvae could digest polyethylene thanks to the presence of two species of gut bacteria, dubbed Enterobacter asburiae YT1 and Bacillus sp. YP1.
Both studies contradict the long-held idea that polyethylene is non-biodegradable, and point towards a potential biological solution to the massive problems caused by the estimated one trillion plastic shopping bags used every year.
Bertocchini, however, cautions against the discovery being regarded as the only answer available.
“We are planning to implement this finding into a viable way to get rid of plastic waste, working towards a solution to save our oceans, rivers, and all the environment from the unavoidable consequences of plastic accumulation,” she says.
“However, we should not feel justified to dump polyethylene deliberately in our environment just because we now know how to biodegrade it.”
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