Ejection, ingestion and fragmentation of mesoplastic fibres to microplastics by Anax imperator larvae (Odonata: Aeshnidae)

Exposure to plastic litter in ecosystems is increasing globally. Marine and terrestrial ecosystems, as well as freshwater ecosystems, are affected. Despite this, the impact of increased exposure to plastics on the freshwater fauna is largely unexplored. The present work investigates the reactions of 42 Anax imperator larvae to plastics in their habitat. Mesoplastic fibres (ca 8 mm long) were presented with a Chironomus sp. larva that was placed behind the fibre. In the majority of the observations, ejection attempts using the labium and the front legs were observed. When ingestion occurred, macerated plastic fibres (0.5‒3 mm) appeared in the faeces of several individuals. Consequently, Odonata larvae turned mesoplastics into microplastics. It is assumed that the mechanical comminution was achieved by the action of the gizzard, which contains strong chitinous teeth.