Wingspan 8 - 11 mm.
This species is locally abundant on English and Welsh coasts, from Cumbria to Suffolk, on saltings where Saltmarsh rush (Juncus gerardii) grows. It has also been recorded on the Firth of Forth and in Ireland.
The adult is similar to many other whitish species of Coleophora, and examination of the genitalia is advised.
The distinctive larval case, made from a hollowed seed of the foodplant, is unmistakable, but so well camouflaged that the species is easily overlooked, even where abundant. The larva can be found on Juncus gerardii seedheads, both standing and prone on the ground, from late July to May. The plant can be recognised by the shape of its seed (See Collins guide to the grasses, sedges, rushes and ferns of Britain and northern Europe).
Seedheads with feeding holes should be gathered and left in a lidded container for the larvae to disclose themselves by crawling up the sides. Records should not be made purely on the basis of feeding holes, as C. glaucicolella, another species often abundant on saltings, makes similar holes.
Pupation is on a plant stem in May and June. The adult flies in late June and July at night and at sunrise.