Nationally scarce (Nb) on sandy coasts, occasionally inland, throughout much of the British Isles. In Hampshire and on the Isle of Wight recorded from the coastal sandhills of St Helens on the Isle of Wight, and on Hayling Island, with occasional single specimens elsewhere on the coast (MBGBI Vol 4 part 2). Wingspan 9.5-12 mm. Lightly marked forms are distinctive. Darker forms might be confused with
C. fraternella (MBGBI Vol 4 part 2).
According to lepiforum.de, the palps are good for identification to species:
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Caryocolum marmorea : brown with white spots, 3rd segment (tip) darker and shorter than 2nd segment
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Caryocolum fraternella : 3rd segment black-brown with white tip, 2nd segment yellow-brown, both of equal length
Larva feeds on Common Mouse-ear and Little Mouse-ear, living within a silken tube or tent.