In Cornwall in the South West of England, this is a dialect
name for a woodlouse, so although not strictly
slang it still owes its origins to dialect and common usage as slang
words do. The difference between dialect and slang is that dialect is not constant, for example just across the Tamar in the county of Devon a woodlouse is ‘chickypig’ while in Somerset it’s ‘gramfy-coocher’ and in Gloucestershire ‘johnny-grump’.