Boreus hyemalis is a very small insect (body length of 3-5 mm) with long legs and downward pointing beak (mouthparts at the end). It is a yellow-brown colour with dark head (no ocelli), antennae and pronotum. The male genital capsule is swollen but not to the extent as Panorpa species. The female has a pale ovipositor. This species is strongly sexually dimorphic. The female has vestigial wings, but those of the males are modified as spines, serrated on the inner edge, to support the female who sites on his back during mating.
The adults are present during winter (active October to April).
Widely distributed in England, Wales and Scoltland, but not recorded in Ireland.