MOST scientific research follows a logical progression, with one experiment following up on the findings of another. Every now and then, however, serendipity plays a part. Such is the case with a paper just published in Current Biology, which reveals to the world a moth that is capable of chewing up plastic.
The experiment behind the paper was inspired when Federica Bertocchini, an amateur beekeeper who is also a biologist at Cantabria University, in Spain, was looking at some of the honeycombs in her hives and noticed caterpillars chewing holes through the beeswax and lapping up the honey. Such pests are not uncommon, so to be certain of what she was dealing with, she collected some of the caterpillars and took them home in a plastic shopping bag for subsequent examination. She assumed the larvae would be unable to escape from this bag, but she was wrong. When, a few hours later, she got around to looking at her captives she found the bag pierced by holes and the caterpillars roaming around her house.
After rounding them up, she identified them as the larvae of the greater wax moth, a well-known pest of bee hives. On considering their escape from their shopping-bag prison, though, she wondered whether they might be put to some sort of use as garbage-disposal agents.
Past attempts to employ living organisms to get rid of plastics have not gone well. Even the most promising species, a bacterium called Nocardia asteroides, takes more than six months to obliterate a film of plastic with a thickness of a mere half millimetre. Judging by the job they had done on her bag, Dr Bertocchini suspected that wax-moth caterpillars would perform much better than that.
To test her idea out, she teamed up with Paolo Bombelli and Christopher Howe, two biochemists at Cambridge University. Dr Bombelli and Dr Howe pointed out that, like beeswax, many plastics are held together by structures called methylene bridges (molecular units consisting of one carbon and two hydrogen atoms, with the carbon also linked to two other atoms). These bridges are impossible for most organisms to break, which is why plastics based on them are not normally biodegradable, but the team suspected wax-moths had cracked the problem.
One of the biggest constituents of rubbish dumps is polyethylene, which is composed entirely of methylene bridges linked to one another. So it was on polyethylene that the trio concentrated. When they put wax-moth caterpillars onto the sort of film it had taken Nocardia asteroides half a year to deal with, they found that holes appeared in it within 40 minutes.
On closer examination, Dr Bertocchini and her colleagues discovered that their caterpillars each ate an average of 2.2 holes, three millimetres across, every hour, in the plastic film. A follow-up test using standard shopping bags weighing just under three grams each found that an individual caterpillar took about 12 hours to consume a milligram of such a bag.
Whether releasing wax moths on the world’s surplus plastic really is a sensible approach to the problem is not yet clear. For one thing, it has yet to be established whether the caterpillars gain nutritional value from the plastics they eat, as well as being able to digest them. If they do not, their lives as garbage-disposal operatives are likely to be short—and, even if they do, they will undoubtedly need other nutrients to thrive and grow. Another question is the composition of their faeces. If the droppings produced by eating plastic turn out to be toxic, then there will be little point in pursuing the matter. Regardless of that, though, the discovery that wax-moth larvae can eat plastic is an intriguing one, for even if the moths themselves are not the answer to the problem of plastic waste, some other animal out there might be.