About Hydrelia sylvata (Denis & Schiffermüller), 1775
Hydrelia sylvata (Denis & Schiffermüller), 1775 has a wingspan of 27–30 mm. The ground colour of the forewings ranges from whitish, greyish white to light beige. Its crosslines are wavy, and coloured either light brown or dark brown; the mid-field crossline is clearly defined. Some specimens have a discal stain, which may be small, indistinct, limited in extent, or absent entirely. The hindwings share the same pattern as the forewings. The marginal lines of both forewings and hindwings are interrupted by veins, forming a series of separate dashes. Pattern intensity and arrangement vary between individuals. The relatively short, stubby caterpillar tapers at both the anterior (front) and posterior (rear) end. Its body colour ranges from purple-red to purple-brown; the front and rear sides are greenish, and the middle section is rose-red. The dorsal line and a series of V-shaped spots on the back are white, while the subdorsal lines are only slightly lighter than the caterpillar's base body colour. Yellow spots are located on the side of the 5th abdominal segment. The small, pointed warts are white with black borders. The small head is dark green and deeply notched. The shiny pupa ranges from blue-green to greenish brown, and has yellow-coloured segment incisions. This species' distribution extends from Iberia and the British Isles in the west, across Central and Eastern Europe, to Siberia, the Russian Far East, and Japan. In Europe, its northern range boundary reaches central Fennoscandia, and its southern range boundary lies along the southern edge of the Alps.
