Caddisfly introduction in Imatra aims to combat midge problem in Finland

In Imatra, South Karelia, the end may be near for pesky biting midges that have troubled residents for years. On Thursday, the Vuoksi area saw the introduction of bottom-skrimshers, a type of aquatic caddisfly that feeds on midge larvae. Along with bottom-skrimshers, smaller relatives known as sieve-caddisflies and stream-caddisflies will also be introduced.

Kari-Matti Vuori, a development manager at the Finnish Environment Institute, released sieve-caddisfly larvae into the Imatra city stream. This initiative aims to help revive an aquatic ecosystem impoverished by the construction of a hydropower plant and water pollution that previously decimated the midges’ natural predators.

Historically abundant in the Vuoksi River, bottom-skrimshers have largely disappeared from the area. The plan is to reintroduce them, with around a thousand larvae currently awaiting placement in the Vuoksi water system. Vuori emphasized that this operation is a world-first experimental endeavor, and while the results remain uncertain, the hope is that these caddisflies will help mitigate the midge issue.

However, the quantity of caddisfly larvae introduced is minimal, and alone they won’t resolve the midge problem, as there are millions of midge larvae in the riverbed. “We will gather clues as to whether this can effectively control the midge issue,” Vuori commented. The larvae were collected from northern parts of the Vuoksi, such as the Lieksanjoki River, and transported to Imatra, where all survived the journey. “We have a good technique for transporting the larvae. I am confident we can diversify the urban stream, even if only slightly,” Vuori concluded.