The Disadvantage of Having a Big Mouth: The Relationship between Insect Body Size and Microplastic Ingestion

Plastic pollution is ubiquitous. When plastics enter natural environments, they break down into microplastics (MPs; <5 mm), becoming more accessible to smaller animals. Insects ingesting plastics in the wild can physically degrade larger MPs into smaller MPs and nanoplastics. While particle size and body size undoubtedly impact plastic ingestion and degradation, we have no predictive understanding of how these factors interact. We studied how a model cricket species (Gryllodes sigillatus) interacts with plastics of differing sizes throughout a 20-fold change in body mass during growth and development. We fed crickets differently sized polyethylene MPs to first investigate whether crickets would avoid MPs when given a choice. We found that they do not. Instead, they gradually began to consume more of the plastic diet over time. Crickets would only consume beads when their mouth size was larger than the MP. While small MPs (e.g., 38 μm) were more likely to be excreted whole, larger MPs (e.g., 425 μm) were more extensively biofragmented if ingested. These effects of insect behavior and body size on the likelihood of plastic ingestion and the degree to which MPs are degraded have important implications for how and when we should regulate size classes of plastic particles entering natural environments.