Brimstone (Gonepteryx rhamni) in Ireland

Ruibheog in Gaeilge. The Brimstone, Gonepteryx rhamni, is Ireland’s only long-lived adult butterfly, living up to twelve months and appearing on the first warm days of spring after winter hibernation.

Identify it in four steps

1. Males lemon-yellow above, unmistakable in flight against hedgerow green; the strongest yellow of any Irish butterfly.
2. Females paler, greenish-white, sometimes taken for a Large White in the field; the hooked wing tips separate them.
3. Both sexes show a leaf-shaped wing profile with a distinct point on each forewing and hindwing.
4. Wingspan 52 to 60 mm; flight is a steady, purposeful cruise along hedges, rarely feeding for long at any single flower.

Habitat in Ireland

The Brimstone is a hedgerow and woodland-edge species tied to its two larval foodplants, Alder Buckthorn (Frangula alnus) and Purging Buckthorn (Rhamnus cathartica). Irish distribution follows Buckthorn distribution, which is patchy: strongest in the midlands raised bogs and Burren limestone country.

Adults overwinter in evergreen cover, particularly Ivy and Holly. On mild February days they can be seen flying long before other resident species emerge. Eggs are laid singly on the underside of Buckthorn leaves in April and May.

Where to see it

• the Burren, County Clare: Purging Buckthorn on limestone pavement supports the strongest western populations.
• Lough Ree raised-bog margins, County Longford: Alder Buckthorn in wet peatland edges holds midland populations.
• Clara Bog, County Offaly: raised bog with Alder Buckthorn in the fen edge; reliable April sightings.

Related species

• Large White (Pieris brassicae)
• Clouded Yellow (Colias croceus)
• Orange Tip (Anthocharis cardamines)