June to early August. Common and well distributed throughout Great Britain with spp. Hepialus humuli thulensis found in Shetland.

Their English name is derived from the males of the spp. humuli which are entirely white, however the females are larger with a striking yellow forewing with distinctive orange markings. The Shetland spp. thulensis is smaller with a creamy white forewing marked with brown. When at rest they hold their elongated wings almost vertically against their body.

The adults have short antennae and have no functioning mouthparts so cannot feed. The males have a swaying flight display which is used at dusk to attract females. The caterpillars can be found from July to May, often overwintering twice as larvae so the life cycle commonly takes two years to complete.