Two potential players in the evolutionary theatre: Do caddisflies mimic gastropods?

Abstract Mimicry is one of the best examples of coevolution. For a mimetic system to function, the mimic has to equal its model. Due to this close dependence, mimetic systems promise deep insights into modes and means of evolution. Mimicry is known to occur in many taxa across different groups of organisms. However, while a plethora of mimetic systems exist, cross‐phyla convergences have only rarely been reported in shelled gastropods. Our literature survey brought to light several mimetic systems including gastropods (as model or mimic), all of them in either a marine or a terrestrial setting. We here report on the first potential case of mimicry involving freshwater snails. We found larval cases of European Helicopsyche caddisfly to closely resemble Valvata gastropod shells in shape and size. In particular, stunning is the detailed similarity of features in these trichopteran cases to those characteristic for snail shells, for example, apex, aperture and umbilicus, hinting at a strong selection pressure to be involved. We discuss this unique case of mimicry that might hold unparalleled insight in mimetic relationships, taking into account alternative environmental factors and potential predatory dupes, in particular birds that might have successively caused the evolution of coiled cases in helicopsychid trichopterans.