06. Aug 2020

Fraunhofer LBF busts the caterpillar myth: biodegradation of PE by wax moth larvae unproven

Fraunhofer LBF busts the caterpillar myth: biodegradation of PE by wax moth larvae unproven

It was an attractive idea, but was it true? A few years ago, the first reports of wax moth caterpillars being able to eat and digest plastic surfaced in the press. The news was received with excitement, with some even hopefully talking of a breakthrough in plastic waste management.

Can the larvae of the wax moth Galleria melonella really contribute to a CO2-neutral solution to the mountains of plastic waste accumulating worldwide?

Researchers at the Fraunhofer Institute for Structural Durability and System Reliability LBF thought the matter was worth a closer look, as no one was really sure what the larvae were doing, and how they were doing it.

A study published early 2019 reported found that the larvae ate PE at a voracious rate: 100,000 caterpillars could eat about 5.2 kilograms of PE in a single week. This could open up promising possibilities for the disposal and elimination of large quantities of plastic waste. However, before this remarkable ability of the caterpillar can be harnessed technologically, it must be established whether it actually digests the PE - or merely crushes and excretes it.

Within the framework of a research project on the chemical imaging analysis of plastic digestion in caterpillars (RauPE), a team from Fraunhofer LBF used high-resolution Raman microscopy and dedicated software to follow the path of the plastic through the caterpillar.

Using state-of-the-art, high-resolution Raman microscopy and dedicated software for Raman microscopy of mixtures in Python, the Fraunhofer LBF team was able to spatially visualize low concentrations of plastics within a mixture of different organic substances inside the caterpillar. This is possible in three dimensions, with a resolution of up to one micrometer (0.001 mm). By using confocal optics, scientists could study caterpillars non-destructively, i.e. largely without preparation.

The results so far have amazed the project team: caterpillars eat holes in PE foil, take in small amounts of it, losing considerable body mass in the process. Once there are holes, the caterpillars stop further material intake.

The analytical measurement data provides no evidence that the caterpillars digest the polyethylene.
“The fact that caterpillars biodegrade polyethylene remains a visionary goal for the time being, and intensive interdisciplinary efforts are essential to achieve it. For scientific research, it is therefore all the more important to avoid and recycle plastic waste, taking into account all stages along the packaging value chain,” said Dr. Bastian Barton, who supervised the research project at Fraunhofer LBF.

There is an urgent need for improved concepts and suitable technologies for the production of post-consumer plastics with high quality and constant availability. Only then would it be possible to reuse plastics already in use on a large scale and for a wide range of products, noted Barton.

The Darmstadt researchers have also documented the RauPE research project in a video.


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