Marsh Fritillary on the Lizard spring ©P.Eeles R.J. Curtis & I.M.D. Maclean The Marsh Fritillary (Euphydryas aurinia) The Marsh Fritillary is one of our most attractive and rarest butterflies. They are characteristic of damp grasslands and more brightly patterned than other Fritillaries, with wings chequered orange, cream and black. It was once widespread in Britain and Ireland but has declined severely over the last century – it is now one of the most rapidly declining butterfly species in Europe, and fully protected under European and British legislation. The principle reason for the decline is because many of the wet meadow habitats have been drained for agriculture, although scrub encroachment through lack of management and climate change are also potential factors. ©P.Eeles A Stronghold in the Southwest In England, the Marsh Fritillary is predominantly restricted to the wetter, south-western counties. There are probably only a dozen or so colonies in Cornwall. Although some large populations remain around Bodmin Moor, many colonies are very small supporting only tens of adults. Recently, Marsh Fritillaries have probably become extinct in West Penwith, and populations have plummeted around former stronghold sites (e.g. Goss Moor). There are approximately a handful of colonies on the Lizard, although several sites support quite large populations. This leaflet provides information about the Marsh Fritillary on the Lizard, and how to ensure that they remain a feature of the Cornish landscape. © Data copyright Butterfly Conservation 2016 Life Cycle Adult butterflies normally emerge during May, although the date varies depending on the warmth of the spring. Like most butterflies, there has been a noticeable advance in emergence dates with climate warming. Males emerge first, and patrol their territories with low zig - zagging flights while searching for freshly emerged females with which to mate. ©D. Batchelor Females are noticeably bigger although slightly paler than males, and most conspicuous when gravid with eggs – she carries so many that she is barely able to fly. She searches for suitable Devil’s-bit Scabious plants and lays her eggs in batches on the underside of the leaves. The eggs hatch after a few weeks and the gregarious larvae spin a protective web around the scabious on which to bask and feed communally. Although they have few predators, they are attacked by a parasitic wasp which can cause high larval mortality. In autumn the larvae spin a hibernaculum with much denser silk which insulates and protects the caterpillars during the winter. Indeed, on wet sites they can even survive being submerged for several weeks. They re-emerge early the following spring (late February / early March) and the webs and ©P.Eeles larvae become very conspicuous against the low winter vegetation. After several weeks the larvae become solitary and disperse widely. Pupae are formed in low vegetation and adults emerge a few weeks later. Research on the Lizard The University of Exeter is currently conducting research on Marsh Fritillaries on the Lizard with three primary aims: To identify the locations of all remaining colonies, and to estimate population size. To understand the determinants of distribution and abundance at these colonies - why do they occur where they do? To use this research to conserve remaining populations, and to inform landowners how best to manage these sites to maximise population levels. Population size is calculated by counting the number of larval webs during February and March, when the post diapause larvae are most conspicuous. In 2016 all potentially suitable sites were surveyed for larval webs, but no more than a handful of colonies were discovered, and several of these were quite small. ©C. Lumsden Research has shown that Marsh Fritillaries have distinct habitat preferences. Most importantly seems to be the availability of the sole hostplant, Devil’s-bit Scabious. The large numbers of communal larvae quickly devour the plant on which the eggs were laid, and so often have to travel relatively large distances to find food. This problem is exacerbated in the following spring when the larvae undergo continued bouts of feeding to sustain several weeks of rapid growth – starvation is a frequent cause of mortality. ©J. Bacon Secondly, this butterfly shows a preference for unfertilised grassland habitats which have an intermediate turf height ranging from 5 – 25cm tall, so both tightly grazed and unmanaged sites are rarely occupied. Thus there is a danger associated with both over and under managing Marsh Fritillary sites. Conservation The Marsh Fritillary is one of the most seriously threatened butterfly species in the U.K. Wide-scale habitat destruction and degradation of unfertilised grasslands now means that most Marsh Fritillary colonies exist as metapopulations (separate populations connected through dispersal). However, females are generally poor dispersers, colonising sites further and further away only as their egg load lightens. Furthermore, as an occupier of mid successional habitats many colonies are also ephemeral, utilising sites containing early successional vegetation and vacating them when they become overgrown. Therefore its continued survival is reliant on maintaining and improving a close-knit network of low intensity livestock farmed sites across the landscape. Previous research undertaken by Butterfly Conservation across England has shown that: 90% of occupied sites contain locally abundant Devil’s-bit Scabious. However, height and structure of vegetation is extremely important, with larvae often found at the boundary between long and short vegetation. Creation of a mosaic sward is thus a paramount management objective. Overgrazing caused a decline in 37% of sites, with the best sites using cattle (0.1 – 0.4 livestock units / hectare / year) of approximately one suckler cow per hectare for 3 months of the year. Ponies are also suitable, but sheep create a tight sward which prevents scabious plants from germinating and so are generally unsuitable. Too little or no management caused extinction on 35% of sites. Both coarse grasses and scrub shade out Devil’s-bit Scabious. Therefore, scrub cover should be kept at 5 – 10% (although a higher amount on high or exposed sites is fine), cut and removed between October – March, and ideally managed on rotation. Mowing is generally unsuitable (prevents a mosaic structure of vegetation), although small scale burning in early spring can be beneficial, especially if combined with grazing. However, large scale burning is likely to destroy colonies. Climate change is potentially a threat to this species, as warmer temperatures could mean damp habitats could become progressively drier, and vegetation growth rates increase expediting the dominance of coarser grasses and scrub. The recommended management of creating a mosaic vegetation structure can ameliorate the impact of climate change and is beneficial to many other species which inhabit grassland habitats. ©G. Richardson ©P.Eeles ©P.Eeles The Importance of Habitat Structure. Like many butterflies, the key to conserving populations of Marsh Fritillaries relies on maintaining suitable habitat quality for the larvae. This is the longest and most vulnerable stage of the life cycle and larval survival is therefore reliant on the amount of Devil’s–bit Scabious and the structure of habitat that surrounds them. Habitat structure is important as the larvae need to raise their body temperature to approximately 35 degrees Celsius to maximise the efficiency of a gut enzyme in order to digest their food. Larvae thus require small patches of taller vegetation which can support the construction of a silken web which the larvae use to bask communally, thus raising their body temperature more effectively within a group compared to individually. These basking platforms are created with a southerly aspect, and the black larvae align themselves in neat rows to maximise the warmth of the weak, early spring sunshine. Once their food is digested they move off the webs and resume feeding. By March and April the larvae moult into their fifth and sixth instars which have a row of highly reflective silver spots along the length of their bodies. This allows larvae to reflect as well as absorb heat, and with the warmer spring sunshine they can now self-regulate their own body temperatures so communal basking is unnecessary and the larvae become solitary. Creating a structurally diverse habitat within sites is therefore an important factor in managing Marsh Fritillary colonies. ©R.Curtis Basking Marsh Fritillary larvae as seen through the lens of a thermal camera. Note an individual larvae at the front of the group is starting to move away to resume feeding. Fire as a management tool. Used correctly, the use of fire can significantly enhance site condition for the benefit of Marsh Fritillaries. However, misuse and extensive burning can be severely detrimental and is frequently responsible for local extinction of small populations. Marsh Fritillaries are in the larval stage from June – April. The most important factor is therefore to burn CLOSE TO, NOT ON areas of habitat where they occur (e.g. at least 30 meters or so away). Historically there are numerous examples of the inappropriate use of fire causing local extinctions by burning too close to colonies. Ideally, several small areas should be burnt (e.g. ideally from 50 - 1000m2), thus creating a patchwork of heterogeneously diverse habitats, essentially providing areas for egg-laying, roosting and feeding (nectar plants) all within close proximity. Areas should be burnt on rotation (every few years) to allow time for Devil’s-bit Scabious to grow (female Marsh Fritillaries select plants for egg-laying on the basis of prominence and number of leaves). There is evidence to suggest that a rapid burn with the wind will cause less damage to Devil’s-bit Scabious plants, reducing the time for this newly burnt area to become suitable for egg-laying. Burning should generally occur during January and February, and fire breaks should be utilised to ensure only the designated area is burnt.