The Campion Sideridis rivularis
Wingspan 27-30 mm.
Distributed widely over much of Britain, and fairly common in places, the species can closely resemble The Lychnis (H. bicruris), but tends to have the two forewing stigmata joined at the base. Fresh specimens usually also have a purplish suffusion.
It mainly flies in May and June, but in the south there is a second brood in August and September.
The caterpillars feed internally in the seed capsules of various campions (Silene) and catchfly (Lychnis).