The marsh fritillary (Euphydryas aurinia) is a butterfly of the family Nymphalidae. Commonly distributed in the Palearctic region, the marsh fritillary's common name derives from one of its several habitats, marshland. The prolonged larval stage lasts for approximately seven to eight months and includes a period of hibernation over the winter. The larvae are dependent on the host food plant Succisa pratensis not only for feeding but also for hibernation, because silken webs are formed on the host plant as the gregarious larvae enter hibernation. Females lay eggs in batches on the host plant and are, like other batch-layers, selective about the location of oviposition because offspring survivorship levels for batch-layers are more tied to location selection than they are for single-egg layers.
As of 2019 the butterfly's global conservation status is considered of least concern, but it has faced rapid decline and is considered regionally vulnerable or endangered over much of its range.
Euphydryas aurinia has a wingspan of 30–42 millimetres (1.2–1.7 in) in males. The females are usually larger than the males, with a wingspan of 40–50 millimetres (1.6–2.0 in). These small butterflies are variable in markings and colouration, with many forms and subspecies. The adult butterflies usually show a chequered pattern of brown, orange, and yellow markings. Silver markings are present on the hindwing edge. The underside of the wings is patterned with yellow, orange, and brown without any silver colouration at all. The eggs are yellow, and easily identified because of the large batch size. The larvae are black.
This species is widespread in the Palearctic realm, from Ireland in the west to Yakutia in the east, and to north-west China and Mongolia in the south. The marsh fritillary is in decline in Europe and it is one of eleven butterflies covered by the United Kingdom Biodiversity Action Plan. Within the British Isles, it is more frequent in the south and west, but especially in Wales where there is a stronghold.
This species lives in calcareous grassland, in woodland clearings, in damp marshy areas (hence the common name), and in heathy grassland, dominated by tussock forming grasses, including purple moor and rush pastures. In Finland, E. aurinia has been shown to favor semi-permanent grasslands and impermanent clearcuts in the forest. Young clearcuts were preferred over old clearcuts due to the dense growth of vegetation in old clearcut forests. In the United Kingdom, two types of grasslands can be inhabited by E. aurinia: damp grasslands that are either neutral or acidophilus and dry grasslands that have an abundance of plants growing in lime-rich soil (calcicolous grasslands). These butterflies can reach an elevation of 10–2,200 metres (33–7,218 ft) above sea level.
In the British Isles, the marsh fritillary is usually found in damp, heathy grasslands that are called rhos pastures, from the Welsh word rhos meaning heath. Small populations can be an important element of the ecology because they produce many mobile individuals which can then found other populations. The marsh fritillary is protected under UK law, listed under Schedule 5 of the Wildlife and Countryside Act, and the EU Habitats and Species Directive (Annex II). The Devon Wildlife Trust owns a number of sites at which it monitors this species. Examples include Stowford Moor (near Holsworthy, Devon), Dunsdon nature reserve (near Bude), Mambury Moor (near Great Torrington), Vealand Farm nature reserve (near Holsworthy), and Volehouse Nature Reserve (near Holsworthy). In 2009, population counts had significantly increased from years 2007 and 2008. In 2018, a breeding population was found in Carmarthenshire, Wales, after an absence of 50 years.
In Lithuania (included into the Lithuanian Red Data Book since 2000, red list category-3 (R))(Rašomavičius, 2007) is protected insect species. Euphydryas aurinia usually is found in natural and seminatural moist or wet oligotrophic grasslands (purple moorgrass and heath rush meadows), base rich fens, mostly in Eastern, North-Western and Central Lithuania, where its main foodplant Succisa pratensis (Dipsacaceae) is abundant. Inhabited patches frequently are situated along woodland edges or surrounded by bushes. Species is not found in Southern Lithuania where sandy soils predominate and in South-Western Lithuania where agriculture is very intensive.
Adult butterflies feed on nectar opportunistically, so the density of host plant S. pratensis does not affect adult butterfly feeding. In fact, by the time adult butterflies emerge, S. pratensis does not even flower. Adults are polyphagous and generally feed on Ranunculus ssp., Cirsium ssp., Leucantherum vulgare, Myosotis ssp., Rubus ssp most often. They have also been observed feeding on Caltha palustris, also known as kingcup or marsh-marigold, and Ajuga reptans, also known as bugle or bugleweed.
Euphydryas aurinia is a univoltine species.
Mating is believed to occur randomly, as shown by the fact that there is no significant deviation from the Hardy-Weinberg equilibrium in E. aurinia populations. Adult males display sedentary behavior, perching on bushes or grass. They observe and seek out females. Females mate once in their short lifetime and lay multiple batches of eggs. Due to their short lifetime, females mate soon after they emerge from chrysalis. They bear so many eggs that they are unable to fly far distances until they lay the eggs and only crawl to nearby vegetation. Females are larger and less vibrant in color than males.
As of 2017, rapid decline of the population had been observed in Denmark due to loss of habitat and host plants.
Because the larval stage is highly dependent on the host food plant S. pratensis, decline in the availability of the host plant leads to negative effects on the E. aurinia population. Decline of natural habitats for S. pratensis is correlated with decline in the host plant population. Due to cultivation and shift of land use from traditional farming to grazing, the frequency of S. pratensis populations has declined over the past few years. Damp, basic soil is suitable for high S. pratensis frequency. Environmental changes such as acidification and eutrophication have led to a decline in available optimal habitat for S. pratensis, and consequently for E. aurinia.
As of 2019 the butterfly had become regionally extinct over much of its former range in the UK. The population size in the UK had decreased by 60% over the period during which records have been kept. Human activities such as modern farming altered their main habitat – England's damp meadows – and have changed the climate as well. This loss of major habitats has led to fragmentation and isolation of E. aurinia populations, thus leading to metapopulation formation. E. aurinia is more vulnerable to extinction in the small subpopulations that comprise the metapopulation.
According to the Joint Nature Conservation Committee in 2019, the population has "declined dramatically in Europe and is regarded as endangered or vulnerable in most of its European range," and the remaining populations in the UK and Spain are considered the "European strongholds" for the species.
Major fluctuations of local patch populations of E. aurinia have been reported in western England, with the population number reaching peaks in the 1890s and mid 1920s at population sizes around 40,000 and 1,000 respectively. Despite the massive number of larvae and pupae observed during these two periods of maximal population growth, the population frequency of E. aurinia fluctuated drastically as the number of caterpillars observed dropped as low as 16 caterpillars in 1920 after a "diligent search". Thus, E. aurinia serves as a good indicator of environmental changes due to its vulnerability to habitat changes.
As of 2021 the butterfly's conservation status is globally considered of least concern by the International Union for Conservation of Nature and Natural Resources. However, several areas report regional decreases in population.
