Spalgis epius edged with brownish white of a shade paler than that of the ground colour; both wings with an anteciliary dark brown line with on the inner side a similar edging. Forewing, in addition, with an oval white spot beyond the cell. Cilia of both forewings and hindwings of the same shade as the ground colour of the wings. Antenna, head, thorax and abdomen pale brown, club of antennae ochraceous at apex; beneath: the palpi and thorax brownish grey, abdomen pale brown. Upperside: slightly paler brown. Forewing: the cell and apex darker; a white spot similar to that in the male
Pale crag martin often treated as the small, pale northern subspecies of the rock martin, but it is now usually considered to be a separate species. The changes in size and colour are continuous, so the evidence for separate species is not strong, although some rock martins can weigh more than twice as much as the smallest subspecies of the pale crag martin. The average weight for "P. o. fusciventris" is 22.4 g (0.79 oz) against 10 g (0.35 oz) for "P. o. obsoleta". There do not appear to be any intermediate forms where pale crag martins and rock martin populations breed close