Marsh Fritillary Butterfly

By Aisling Natoff, Junior Ecologist, IRD Duhallow

The Marsh Fritillary (Euphydryas aurinia) is one of four Fritillary butterflies found in Ireland. It is the smallest of these four with a wingspan ranging from 35 to 50 mm. The upper-side of the butterfly is chequered with orange, brown and cream patches, and the paler underside is chequered with just orange and cream. A distinguishing characteristic of the Marsh fritillary is a band of orange patches with a black dot centering each patch at the base of their underwing on either side.

The Marsh Fritillary is univoltine, meaning it produces only one brood of eggs per season and in Ireland, can be found on the wing between mid-May and mid-July. The caterpillars are monophagous, meaning they feed solely on a single species of Larval food plant, and in the case of Marsh Fritillary, this plant is Devil’s-bit Scabious (Succisa pratensis). As such, eggs are laid on the underside of Devil’s-bit scabious leaves, with their large brood allowing them to lay up to three batches of around 300 eggs across a habitat.

Caterpillars hatch some four to five weeks after eggs are laid, and go through six growth periods known as instars which is followed by pupation when they form a chrysalis. Caterpillars spend their first three instars feeding on the larval food plant in groups. By Autumn they have reached their fourth instar, at which point they turn black and begin to build a dense web at the base of the Devil’s-bit scabious plant for overwintering before feeding can resume in Spring. The fifth instar occurs in early spring and is spent basking in groups and feeding on Devil’s-bit scabious. During the sixth instar they disperse from the larval plant before pupation begins.

The Marsh Fritillary is one of six threatened Irish butterflies, classed as vulnerable to extinction under the Irish Butterfly Red List. It is listed under Annex I of the EU Habitats Directive, making it the only protected butterfly species in the Republic of Ireland. They have a wide distribution across the country; however their numbers are declining due to habitat degradation resulting in a loss of suitable feeding and breeding grounds containing Devil’s-bit Scabious which they rely on to survive. Suitable habitat for Marsh Fritillary include semi-natural grasslands, especially calcareous grassland, degraded bogs, wet heath, and fens up to 300m.

Monitoring of habitats that are and once were suitable for Marsh Fritillary is vital to track changes in their population and further understand threats they face. In particular the monitoring of their known breeding sites is of great importance, and citizen science plays a big role in this. Such monitoring is organised by the National Biodiversity Data Centre in collaboration with the NPWS. Once a year volunteers are gathered to survey suitable breeding sites between August and mid-September in which a predetermined route is walked in order to find and record the presence of Marsh Fritillary Larval webs, as well as carry out a habitat assessment in which the abundance of Devil’s-bit Scabious is recorded.

For more information on the Marsh Fritillary Monitoring Scheme, visit the National Biodiversity Centre website at https:// biodiversityireland.ie/surveys/ marsh-fritillary-monitoring-scheme/

Devil's-bit Scabious