These are greyish or brownish caddisflies with pale mottling and darker blotches. The antennae is as long as the body. Forewing length 10 to 12mm.
They fly June to September, and are seen near streams and rivers. Attracted to light. Common and widespread throughout.
Photograph of Grey Flag (Hydropsyche siltalai), taken July 2015, rear garden , Staffordshire. © Pete Hillman 2015. Camera used Nikon D3200, with Sigma 105mm macro lens.