Insect larvae create plastic pollution through habitat formation, find researchers

11 Oct 2022 --- Researchers from the University of York, UK, have discovered that the larvae of Caddisflies – a common insect that inhabits global freshwater environments such as rivers, lakes and ponds – contribute to microplastic pollution by disintegrating larger pieces of plastic trash to build protective casings in which they can live. 

“The active use of plastic litter by freshwater animals that our study uncovered could contribute to the formation of microplastics within these habitats,” says lead author of the study, Ph.D. student Katey Valentine from the department of environment and geography at the University of York. 

Co-author of the study, professor Alistair Boxall, says: “As well as demonstrating microplastic production, our work also shows how these organisms can exploit plastics to construct their homes. This could make the larvae more prone to predation and result in increased exposure to things like additives that will slowly leach from the plastic.” 

“Further work is now needed to determine the extent to which these animals could be utilizing plastic litter and creating microplastics throughout natural freshwater environments globally, and whether other common freshwater species exhibit similar behavior,” adds Valentine. 

The scientists found that the larvae used their sharp teeth to bite plastic into smaller pieces to build protective casing. Larvae casings
The scientists found that the larvae used their sharp teeth to bite plastic into smaller pieces, which they then used to build the protective casing they live in until they are ready to transform into adult flies. 

Researchers have found microplastic everywhere, from the deep sea to the Antarctic ice, in plants and food, as well as in the human body through blood and breastmilk. Yet, they don’t know if these particles are dangerous, but the risks are thought to be high. 

“Given the increasing concern for the effects of plastic pollution on our environment, we wanted to understand whether caddisfly larvae would interact with items of plastic litter which commonly pollute the environment, and determine what the consequences of these interactions might be,” explains Valentine. 

Oak vs. polyester
Caddisfly larvae usually use natural materials such as sand, gravel and plant debris to build their protective casings, weaving pieces together using self-produced silk, explain the researchers.

For the study, they presented larvae with pieces of plastic film cut from a commercially available biodegradable plastic bag, alongside pieces of oak leaf. Although larvae generally tended to use more of the oak leaf material, the scientists say that many larvae used pieces of plastic to build their new case while leaving suitable pieces of leaf material untouched.

The plastic film used for the experiment was made from a bio-based polyester traditionally marketed as a biodegradable alternative to conventional plastic – which has led to its increased use in food packaging and agricultural mulching films as an “eco-friendly” alternative. 

However, despite being biodegradable in industrial composting systems, in aquatic environments, the degradation of this plastic is reported to be “extremely slow” and it is therefore thought to pose a similar pollution risk as conventional plastics.

By Natalie Schwertheim