Marsh fritillary


The marsh fritillary 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.

Taxonomy

E. aurinia is represented by many subspecies. The most widely accepted are:
  • Euphydryas aurinia aurinia central Europe, southern Europe, western Siberia
  • Euphydryas aurinia bulgarica Carpathian Mountains
  • Euphydryas aurinia laeta central Siberia, Altai, Sayan, Transbaikal
  • Euphydryas aurinia beckeri Morocco submarginal band of the hindwing is of a magnificent deep russet-red colour and nearly occupies the whole outer half of the wing, being outwardly bordered by black lunules centred with pale yellow
  • Euphydryas aurinia barraguei Algeria
  • Euphydryas aurinia provincialis
  • Euphydryas aurinia debilis Mountainous areas like Pyrenees and Alps
but the total number of described subspecies is much higher, especially in the eastern Palaearctic. The insect may be best considered a superspecies.
E.aurinia is in the subgenus Eurodryas The clade members are:
  • Euphydryas aurinia
  • Euphydryas provincialis
  • Euphydryas orientalis
  • Euphydryas asiatica
  • Euphydryas sibirica
  • Euphydryas laeta
  • ''Euphydryas desfontainii''

    Description

Euphydryas aurinia has a wingspan of in males. The females are usually larger than the males, with a wingspan of. 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.

Distribution and habitat

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, 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. These butterflies can reach an elevation of 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. The Devon Wildlife Trust owns a number of sites at which it monitors this species. Examples include Stowford Moor, Dunsdon nature reserve, Mambury Moor, Vealand Farm nature reserve, and Volehouse Nature Reserve. 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 is protected insect species. Euphydryas aurinia usually is found in natural and seminatural moist or wet oligotrophic grasslands, base rich fens, mostly in Eastern, North-Western and Central Lithuania, where its main foodplant Succisa pratensis 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.
In Croatia, it is only present in the north, and even those findings are only historical. Attempts to confirm its presence have failed, but northern Ivanščica and the Lobor valley are considered promising.

Factors for optimal habitat

The availability of larval food plant S. pratensis and grass height are the most important factors in providing an optimal habitat for E. aurinia.

Host plant availability

Because caterpillars live in communal webs formed around their host plant and hibernate through the winter inside the web, the density of host plant is a crucial factor in forming the habitat of E. aurinia. Studies have shown that the density of host plant is directly correlated to the number of larval webs found, which in turn is directly related to the number of adult butterflies. Therefore, a habitat suitable for the larvae can indirectly influence the proliferation of adult butterflies.

Sward height

Not only is the density of host plant crucial for a favorable habitat, but also the height of the sward, the expanse of grass covering the area where E. aurinia lives. Sward height that is too short can lead to increased exposure of the larvae to predators and can cause limited food availability, leading to starvation. However, if the sward height is too tall and densely packed, then it becomes difficult for adult butterflies to locate the host plant to oviposit on. Thus, the level of sward height is most optimal when it is medium height.

Food resources

Host plant for caterpillars

The caterpillars are known to feed primarily on Succisa pratensis and species of Digitalis, Plantago lanceolata, Knautia arvensis, Scabiosa succisa, Scabiosa columbaria, ''Veronica, Geranium, Sambucus, Gentiana, Valeriana, Lonicera implexa, Filipendula, Spiraea and Viburnum''.

Methanol emission from feeding

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 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.

Adult feeding

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.

Parental care

Oviposition discrimination

E. aurinia females are batch-layers, meaning they lay a large number of eggs at one site. Because 200–300 eggs are at stake every time an egg-laying site is chosen, batch-laying females tend to undergo a discrimination phase in searching for a location to lay eggs on. Each plant can serve as an egg-laying site for four to five clusters of eggs, meaning that more than a thousand larvae may hatch on a single plant. If so, the newly hatched larvae will face serious food shortage and fierce competition for food, which has huge repercussions for offspring survivorship. Therefore, Euphydryas and other batch-laying females, such as Melitaeini females, spend more time choosing a place to lay eggs and are more selective when looking for a host plant.

Size of host plant and vegetation density

Female oviposition depends largely on the size of host plant as well as density of vegetation cover. Studies have shown that females prefer to lay eggs on large host plants as opposed to smaller plants. This is to prevent food shortage and starvation of the larvae. Also, sparse, open vegetation structure is favored over dense, thick grasslands when the host plant S. pratensis is used for oviposition. The presence of a tall non-host plant is negatively correlated with egg nests. Therefore, abandoned meadows with lime-rich soil have been identified as oviposition sites. Often, E. aurinia will lay eggs at edges of such meadows because the vegetation structure and plant height fit the female butterfly preference for oviposition. For such reasons, croplands are generally favored over meadows for oviposition because croplands tend to have concentrated numbers of large-sized host plants.