On warm days in the winter the larvae sometimes leave their hiding-places and are then found on fieldpaths and roads, running about quickly.

The ruby tiger has the thorax and forewings dark reddish brown with a blackish comma-shaped spot at the apex of the cell, edged with carmine.

[5] The name-typical form ''Phragmatobia fuliginosa L. has the forewing rather densely scaled and the hindwing bright rose-red with distinct black spots.

[5] Phragmatobia fuliginosa borealis has vivid black markings and the red is confined to the sides of the abdomen and the anal part of the hindwing.

subnigra Mill., that has very dark forewings, must not be confused with the northern form; it is scarcely darker than true fuliginosa, and not so strongly hyaline as borealis.

[7] The caterpillars are polyphagous, feeding on various plants, mainly Rubus fruticosus, Prunus spinosa, Filipendula ulmaria, Plantago lanceolata, Senecio jacobaea, Salix repens, Salix starkeana, Salix phylicifolia, Polygonum spp., Rumex crispus, Potentilla erecta, Rubus idaeus, Trifolium spp., Chamaenerion angustifolium, Calluna vulgaris, Vaccinium myrtillus, Vaccinium uliginosum, Andromeda polifolia, Plantago major, Taraxacum vulgare and Taraxacum officinale.