Nettlemas is a former Irish custom previously associated with the first of May. The preceding day, 30 April, was called "Nettlemas night".
The custom is mentioned in Samuel Carter Hall's Ireland, Its Scenery, Character &c (1841), where it is described as "peculiar to Cork".[1] Hall writes that, on Nettlemas night, boys in Cork walked in the streets stinging one another with nettles.[1][2]
In Ireland's Wild Plants – Myths, Legends & Folklore (2017), author Niall Mac Coitir suggests that this folk custom was associated with "southern parts of County Cork" and compares it to a similar tradition, known as "Stinging Nettle Day", in South West England.[3] Other sources describe similar customs in parts of Scotland, Devon and Cornwall.[4]
Another old custom prevails also to some extent. May eve, the last day April, is called "Nettlemas night;" boys parade the streets with large bunches of nettls, stinging their playmates [..] These are the only customs peculiar to Cork
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In southern parts of County Cork, May Eve (30 April) was known as "Nettlemeas Night" when boys would parade the streets with large bunches of nettles, stinging their playmates [..] Similar customs were found in Devon and Cornwall, where May 1 (or 2) was known as "Stinging Nettle Day"