Guest blog by Katy Bell, RSPB NI'S Pettigoe Project Officer (CABB)

The marsh fritillary (Euphydryas aurinia) is one of three fritillary species we get in Northern Ireland. It is much smaller than the other fritillaries, the dark-green and silver-washed, and is much less common. This species has declined rapidly across Europe and is classed as vulnerable. It is a Northern Ireland Priority Species and is protected under European Law.
Across the UK, they have declined massively since the 1970s and are now restricted to the west coast of Scotland, south and west Wales, Northern Ireland and south west and central southern England. Northern Ireland is now a stronghold for the species and since the warm summer in 2018 there has been an increase in the number of breeding sites recorded.

Across the country, it is found in small isolated sites, with Murlough Bay being one of the best populations in County Down, and County Fermanagh having a strong population. It was known to be a butterfly of wet grasslands, hence the name, but it can also be found in dune systems, bogs and the edge of fens.
Now is the best time of year to see the adult butterflies as they are only on the wing for a short time. They spend the majority of their lives as caterpillars. In late May and early June, if you are lucky enough to be outside on a sunny day, then look for fast-flying marsh fritillaries flitting from flower to flower. This is when the adults will be feeding, mating and then laying their eggs for the next generation.

On the island of Ireland, the caterpillar has only one food plant; devil’s-bit scabious (pictured, above). This species used to be widespread but due to changes in agricultural practices it isn’t as common now to see fields full of this beautiful plant. The butterflies lay their eggs onto the leaves of devil’s-bit scabious plants throughout June and July and these then hatch out in July and August and feed on the leaves.
They exist in little communities of larval webs’ where they feed and move as a group. There may be hundreds of caterpillars in one larval web (below).

August/September is the official time to survey the caterpillars. The caterpillars will keep feeding until early winter when they will prepare for hibernation. They will remain in their hibernation web low in the vegetation over the winter. In February, on mild sunny days, they will emerge again and continue to feed and bask in the sunshine. By the end of March, they disperse and in April/May they will find a sheltered spot to pupate. The adults will emerge in late May and June and start the process over again.
Last year we had two great discoveries. In February, as part of the Co-operation Across Borders (CABB) project*, a new breeding population was discovered on the edge of Pettigoe Plateau SAC in Fermanagh. RSPB NI is now working in partnership with Butterfly Conservation to make sure this farmer’s land is kept in perfect condition for the species. We carried out an official survey in September and recorded 37 webs in total. This makes it one of the most productive sites in Northern Ireland.

In September we also visited the RSPB Lower Lough Erne Islands reserve and were astonished to find seven webs. This is the first time the species has bred on an RSPB reserve in Northern Ireland and only the fifth in the whole of the UK. These populations are near to each other and we hope to create a network for the species which is essential to maintain a sustainable population. These areas are now being grazed and managed specifically for marsh fritillaries.            
Montiaghs Moss, which is also part of the CABB project along with Pettigoe, has been a long-established marsh fritillary colony with it first being recorded in 1993, and being recorded annually since 1990 (apart from 1997). Monitoring breeding populations, by counting larval webs in September, to assess the condition, size and viability of the species began in 1999. This allows us to understand what is going on with the species and identify trends. Marsh fritillaries have been recorded on the wing in Montiaghs in the past week.

In the past Montiaghs Moss was cut for turf which has left a complex mosaic of peat ramparts, trenches wet woodland, wet heath, meadows and fen. In 2003 it was estimated that one percent of the sward was Sucissa pratensis and less prevalent today. In 2018 Butterfly Conservation recorded 40 larval webs and with the CABB project, RPSB NI and BCNI are reinstating management to benefit this and other species found at the Montiaghs. We’ve already repaired boundary fencing so the meadows can be safely grazed with cattle. This will benefit the marsh fritillary as it likes a varied sward structure between 15cm and 25cm, easily achieved with cattle. Some willow and Alder Scrub is due to come to reduce shading of the foodplant.
A habitat which is managed for marsh fritillaries will also benefit a host of other invertebrate species. It is such a charismatic little butterfly and we want to see it flying over our grassland meadows and dunes for years to come.

All photos by Katy Bell

NOTE: A licence is needed to survey marsh fritillaries in Northern Ireland. This can be obtained from the NIEA website. If you think you have marsh fritillary on your land then contact NIEA or Butterfly Conservation.

* The Co-operation Across Borders for Biodiversity (CABB) project is supported by the European Union’s INTERREG VA Programme and managed by the Special EU Programmes Body (SEUPB). The €4.9m (£4.3m) project is being delivered through a partnership between RSPB NI (the lead partner), RSPB Scotland, BirdWatch Ireland, Butterfly Conservation, Northern Ireland Water and Moors for the Future. The project spans Northern Ireland, the Republic of Ireland and Scotland will improve habitats for birds, butterflies and other species, restore blanket bog and help produce drinking water at a lower cost.