Wingspan c. 12 mm.
The larval case of Coleophora genistae is built in a distinctive herringbone like fashion, and is sometimes likened to a spikelet of certain grasses.
The foodplant is petty whin (Genista anglica) the larva feeding on the leaves, and sometimes the flowers. The leaves are blanched by the feeding, and the species often feeds gregariously, becoming a pest.
The adults fly from June to August, and have brownish forewings with a white costal streak.