Caddisflies Stenopsyche marmorata (Trichoptera: Hydropsychidae) exploit river mussels as anchors for their nets

In the foothill rivers of the south of Primorsky Krai (Russian Federation), during the abnormally hot summer-autumn season of 2021, the number of net-spinning larvae of the caddisflies Stenopsyche marmorata Navas, 1920 (Stenopsychidae) sharply increased. Here we describe the phenomenon of widespread use by these caddisfly larvae of the shells of live bivalves Middendorffinaia Moskvicheva et Starobogatov, 1973 (Unionidae) to attach their feeding nets. As a result, the immobilized river mussels could not move to the deeper sites for wintering, and in the coming winter season they died due to freezing into ice. The described phenomenon illustrates the indirect negative impact of climate change on vulnerable species of river biota.