Although Robson was aware of the two forms of this species, the differences in their life histories had not been fully elucidated in his time. ssp. Quercus. Linn., 1758. Oak Eggar- The lowland form, feeding on a variety of hedgerow and woodland plants and completing its life history in one year, has this designation. It used to be found on the Durham coast from Hartlepool to Marsden, but there have been no reports since the 1930's, when it was known on the cliffs just north of Crimdon Dene (now covered with holiday chalets). [...] otherwise all records since the 1930's refer to the larger, darker:- ssp. CALLUNAE Palmer, 1847. Northern Eggar. This form has a two-year life cycle, the larvae feeding on heath and moorland plants (usually Calluna vulgaris), in which habitat the Northern Eggar is widespread and common [...] Larvae tend to be recorded more frequently than the fast-flying imagines, as they are large and conspicuous when feeding on heather. The males are normally diurnal in flight, but both sexes are occasionally taken in light traps (females more often than males).