Marsh Fritillary

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. …

One study measuring the level of volatiles released by plants that are consumed by herbivores has shown that huge amounts of methanol and other volatile substances (monoterpenes, sesquiterpenes and lipoxygenase-derived volatile compounds) are emitted by E. aurinia caterpillars feeding on the host plant S. pratensis. Methanol is a biochemically active compound that is commonly released by metabolic activities of anaerobic bacteria.