100-million-year history of caddisflies (Insecta: Trichoptera) as hosts of trematodes

This study explores the intricate parasitic relationship between a caddisfly larva and a trematode preserved in mid-Cretaceous Burmese amber. Through detailed morphological analysis, the caddisfly larva is classified within the suborder Integripalpia, closely resembling the family Calamoceratidae. Likewise, the parasite, exhibiting traits consistent with flatworms of the phylum Platyhelminthes, is tentatively identified as a digenean trematode. The discovery of ectoparasitism, where the trematode firmly attaches to the caddisfly larval exterior surface, challenges conventional understandings of trematode behavior, suggesting a departure from typical endobiotic lifestyles. The first finding of fossil flatworm parasitism on an aquatic insect sheds light on the evolutionary flexibility of trematodes and their ability to exploit diverse ecological niches. Moreover, the complex parasitic lifecycle, involving intricate stages from egg release to host transmission, underscores the complex interactions between organisms in ancient ecosystems.