The Marsh Fritillary (Euphydras aurania) is Ireland’s only legally protected butterfly and is afforded protection under Annex II of the EU Habitats Directive, the Bern Convention and the Wildlife Act 1976, as amended. Marsh Fritillary is categorised as ‘Vulnerable’ under the Red List of Irish Butterflies, meaning it is considered at high risk of extinction. The Marsh Fritillary has a wide but patchy distribution across Ireland. It has experienced a severe population decline in recent decades due to the loss of suitable habitats such as uncultivated grasslands, overgrazing on remaining habitat, and its requirement for specific habitat areas and wildlife corridors.
Of the four fritillary butterfly species present in Ireland, the Marsh Fritillary is the smallest, with a wingspan of between 35-50 mm and is also the most brightly coloured. It can be identified by the orange and cream chequered pattern against a brown background with distinctive cream bands on the underwing. Apart from a slight size difference, male and female Marsh Fritillaries are similar in appearance, but until they have laid their eggs, the females are easily identified by their swollen abdomen.
Colonies of these butterflies can occur in different habitats, including sand dunes, calcareous grassland, fens, bogs and upland heaths and grasslands. The occurrence of the Marsh Fritillary is dependent on the presence of its main food source, Devil’s-bit Scabious (Succisa pratensis), and the long-term survival of the Marsh Fritillary is dependent on extensive grazing, ideally by cattle, which maintains its habitat in good condition. Being an Annex II listed species under the EU Habitats Directive, the habitat of the Marsh Fritillary is currently protected within Special Areas of Conservation, which is listed as a Qualifying Interest.
Marsh Fritillary butterflies need large areas of suitable habitat (ideally more than 50 hectares) to maintain a sustainable population as it cannot survive long-term if the only habitats available are small and isolated. Their populations have been described as ‘boom and bust’ as their numbers can explode one year, and then they may almost vanish the next, gradually building up numbers again over the ensuing years. In some years, colonies expand and can be found in new locations or habitats that appear less than ideal. The colonies can experience crashes and contract to ‘core’ sites in other years. These fluctuations may be due to poor weather, the condition of the breeding sites, or parasitic flies and wasps whose larvae feed on the caterpillars of the Marsh Fritillary.
Marsh Fritillary eggs are laid shortly after the emergence of the females in mid-May. The eggs are laid on the underside of Devil’s-bit Scabious’s basal leaves, and the larvae hatch from the eggs from early to mid-June. The larvae spin a web close to the ground on these leaves, and these webs become enlarged over time and much more noticeable from August onwards. By late September, the webs are very visible. The larvae construct a similar web where they will over winter and emerge in spring, generally in mid-March. The individual larvae will form pupae attached to a twig or grass stem close to the ground from late April to early May. Adult butterflies emerge from late May to late June to begin the cycle again.
At MKO, our Ecologists undertake marsh fritillary surveys for proposed developments throughout Ireland. Marsh Fritillary surveys are generally required if there are existing desk study records for the locality, if areas of particularly suitable habitat are identified, or if the habitat with which they are likely to be associated has the potential to be affected by a proposed development. Surveys can include detailed habitat condition assessments combined with surveys for adults (in May/June) and larval web surveys (in August/September).
MKO field surveys are conducted in accordance with best practice guidance (NRA 2009) and the National Biodiversity Data Centre (NBDC) Marsh Fritillary survey methodologies for larval web and habitat condition assessments. The optimum survey period for larvae is during August and September, in sunny conditions, when colonies of individuals construct conspicuous webs over Devil’s-bit Scabious leaves and adjacent vegetation. The standard method of monitoring Marsh Fritillary populations is to count these larval webs and record occupied larval webs. Habitat condition assessments then include surveying along a predetermined route for the presence and abundance of Devil’s Bit Scabious as well as recording the vegetation height and any grazing evidence within the study site.