Brimstone

Photo by D O'Brien

Brimstone Gonepteryx rhamni (Linnaeus 1758 )

Family: Pieridae, subgroup Coliadinae (The Yellows)

Description

Photo by Sarah Bradshaw

Photo by Tim Furness

Our only large yellow butterfly: Large White size. The male is distinctively citrus yellow, the female much paler. Confusion with the Clouded Yellow is possible, but that species is smaller (Small White size) and a much richer orange or mustard yellow.

The Brimstone has a small, single, yellowish eyespot on each side of each wing, making the Clouded Yellow’s darker upperwing spots and figure of eight lower wing spots distinctive features.

The female Brimstone is pale enough to be dismissed as a Large White in flight. In closed-wing view the Brimstone is remarkably leaf-like, with the male yellow and the female creamy white and both sometimes tinged with green.

Habitat

Wanderers can and do turn up in every corner of the county. However, breeding concentrations are only found where the foodplants Common (also known as Purging) Buckthorn Rhamnus catharticus or Alder Buckthorn Frangula alnus (formerly Rhamnus frangula) are present.

Purging Buckthorn usually grows into a tree 3-10m (10-30ft) in height. It is found along woodland edges and in scrubby areas and hedgerows, thriving best on poor, dry, chalk and limestone soils but also able to grow on other soils. By contrast, Alder Buckthorn is acid-loving, being found in damp, marshy areas or as an under storey in open woodlands. It grows mainly as a shrub, only occasionally reaching as high as 5-7m (15-20ft).

Distribution

Very mobile, hibernating resident. One brood, with butterfly stage lasting up to 12 months (approx Jul/Jul). The northern limit of the species in Britain lies mainly across Yorkshire and Cumbria, and into Northumberland, with the occasional very rare sighting into Southern Scotland in more recent years.

The majority of tetrad records represent single sightings of wanderers, whilst tetrad clusters indicate areas of foodplant availability where regular breeding takes place. The Brimstone is a butterfly invariably seen one or two at a time and even in its hotspot areas, site counts (covering up to 1km square) are rarely above the 10/30 range. The butterfly has been recorded in every month of the year and increasingly reported earlier (Feb/Mar) and later (Sept/Oct).

2019 was an excellent year with numbers much higher than any in the past 10 years. Good sites in Yorkshire where this species has been regularly seen over the past couple of years are North Cave Wetlands (VC61), Strensall Common (VC62), Brockadale ((VC63), Bishop Wood (VC64), and Nosterfield Nature Reserve (VC65).

Life Cycle

Egg laying sites are carefully selected for warmth and shelter and may be over 4m above the ground. Pale bottle-shaped eggs are placed on the undersides of foodplant leaves or on twigs or buds if leaves not yet open. Most sources indicate that the Brimstone only lays on Buckthorn species.

Eggs are laid from April to July and hatch after about 10 days. Dark green larvae take around a month and 5 instars to mature and usually leave their buckthorn to pupate in low vegetation. Adult butterflies emerge after about 2 weeks and can remain active until the end of Sept or later, building up reserves for hibernation.

The species shows a strong preference for purple flowers when nectaring, and its long proboscis is well-adapted to feeding on flowers like Teasel Dipsacus fullonum. Brimstones often hibernate under evergreen leaves, especially Holly Ilex quifolium or Ivy Hedera helix. They may test the air on warmer winter days and visit ‘Pussy’ Willow catkins Salix sp or early Dandelions Taraxacum hamatum in search of a top-up nectar feed. Brimstones are thought to lay eggs singly, although small clusters are sometimes found and assumed to be the work of several females.

The first Yorkshire sighting in 2019 was 12 February at Carlton Marsh.

The last Yorkshire sighting in 2019 was 29 October at Thorp Marsh.

Photo above left by J Bone

Status

The species is not under threat.

Aberrations

Variation is uncommon with less than 30 aberrations described. Suffusions of orange are possible on the upperwings, and these could give rise to confusion with the Cleopatra. However, such aberrations are extremely rare. Yorkshire reports of the Cleopatra are described in the Rare Species Section of the book.

NF 12/11/20