Caused by the larvae of a tiny gall wasp, Dipoloepis rosae.
Being so prominent and interesting in appearance, this gall has more folklore attached to it than most. The term 'Bedeguar, Bedegar or Bedequar' comes from a French word, bédegar, and is ultimately from the Persian, bād-āwar, meaning 'wind-brought'. Robin in Robin's pincushion refers to the woodland sprite of English folklore.
In Shropshire in the 1880s: ‘If you light on a briar-boss accidental w’en yo’ an’ the tuthache [toothache], an’ wear it in your boasom, it’ll cure it.’
In Wiltshire the gall was ‘often carried in the pocket as a charm against rheumatism‘.
In Wales, a gall placed under a pillow would cure insomnia, ‘but it was necessary to remove it at a given time, or, according to the old story, he would never awake’.
In Northamptonshire in the mid nineteenth century, boys placed a briar-ball in their coat cuffs ‘as a charm to prevent flogging’.
Adapted from Roy Vickery, A Dictionary of Plant-lore, 1995