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Euphydryas Aurinia
The Biology of the Marsh Fritillary
The Biology of the
Marsh Fritillary
Target Species: Marsh Fritillary
Once Common – Now Rare
The Marsh Fritillary is a specialist of nutrient-poor habitats, capable of inhabiting both moist and dry environments through its choice of host plants.
At the beginning of the last century, this species was found in all 16 federal states of Germany and was likely one of the more common species in our historical cultural landscapes. However, the advent of the Haber-Bosch process ended the nutrient deficiency in agriculturally used areas, while the mechanization of agriculture simultaneously increased the intensity of land use. Alongside other factors, such as the loss of floodplains, widespread drainage of landscapes, and the abandonment of traditional land use practices, this led to a rapid decline in the Marsh Fritillary as well as many other animal and plant species.
Today, the Marsh Fritillary is strictly protected under the Federal Nature Conservation Act and is listed in Annex II of the EU Habitats Directive. As an invertebrate species, it has become one of the most important target species for nature conservation in Europe. Due to the Marsh Fritillary’s need for protection, many conservation measures are currently being implemented to ensure its survival. Thanks to the butterfly’s high habitat requirements, the optimization of its habitats indirectly supports the majority of species characteristic of these habitats.
Appearance
As a typical representative of the “checkerspots” (Melitaeini), the Marsh Fritillary has a medium-sized wingspan of about 35 mm and features a distinctive orange-brown-gold checkered pattern. Despite its unique and contrasting coloration up close, the Marsh Fritillary can be mistaken in flight for other frequently co-occurring butterfly species, such as the Nickerl’s fritillary (Melitaea aurelia) or the Duke of Burgundy (Hamearis lucina).
To distinguish the Marsh Fritillary from closely related species in Germany, one can look for its orange-colored submarginal band, which features a row of black spots in the middle on both the upper and lower sides of the hindwings. As with many other butterfly species, females of the Marsh Fritillary are often larger than the males.
Life Cycle
The Developmental Stages of the Marsh Fritillary
For egg-laying, female Marsh Fritillary butterflies choose sun-exposed host plants in sparse vegetation during their flight period from late May to mid-July. They lay 200-300 eggs in a cluster on the underside of large leaves.
The development of the eggs until the larvae hatch takes about 10 days. At the time of laying, the eggs are yellow, but they change color over time to orange, then red, and finally black just before the larvae emerge.
Larval Stages 1-3
After hatching between June and July, the larvae spin a communal feeding web that they continually expand. The web can encompass a single leaf or even the entire host plant. It serves various purposes, including keeping the larvae together, aiding their movement on the host plant, and, most importantly, protecting them from weather and parasitoids. Two species of braconid wasps are more or less specialized on the Marsh Fritillary. Other predators, such as spiders and bugs, can easily overcome the web. Especially during the sensitive molting phases, the larvae gather synchronously in the core of the web. When all consumable parts of a host plant have been eaten, the larvae collectively move to a new host plant and build a new web. On nutrient-poor grasslands with small host plants, despite the larvae’s limited mobility, more than five host plant shifts can occur before overwintering.
Larval Stage 4
At the end of the 3rd larval stage, usually in the second half of August, the larvae molt together again. This time, they construct a particularly dense web called the overwintering web, or “hibernaculum.” The now black larvae spend the entire winter in the hibernaculum. On warm winter days, several larvae may leave the hibernaculum to bask in the sun, but they do not feed. Between February and April, depending on the weather, the larvae begin to build a new communal web and start feeding again. After overwintering, these webs are noticeably looser than before.
Larval Stages 5-6
After molting to the 5th larval stage, which often occurs in smaller groups, the larvae live solitarily until pupation. As the larvae grow, their mobility increases, allowing them to reach more distant host plants. Even when sufficient host plants are available, the larvae often move further away from their overwintering site during their development. This behavior reduces competition for food with other larvae and the chance of being discovered by parasitoids.
In the course of May, at the end of the 6th larval stage and reaching a length of 2.5 to 3 cm, the mature caterpillars seek a location for pupation. A suspended pupa is then formed under leaves or in leaf litter. This stage can last several weeks, depending on weather conditions.
On warm days in May, the butterflies emerge. Typically, the males emerge before the females, increasing the chances of encountering an unmated female. This also allows the males to establish territories, such as small bushes or sun-exposed sections of meadows. The males display territorial behavior, defending their territory against conspecifics and passing insects. Mating usually occurs within the vegetation. The Marsh Fritillary is generally very site-faithful and shows limited dispersal behavior. However, individual butterflies can travel several kilometers. The exact reasons for this behavior are not yet known; possible explanations include density stress or specific weather conditions.
Habitat
Geographical Distribution and
Preferred Habitats
Geographical Distribution and Preferred Habitats
The Marsh Fritillary occurs in Central Europe in two ecotypes. On one hand, the species inhabits a wide range of oligo- to mesotrophic wet meadows and fenlands, and on the other, it also occupies dry habitats such as calcareous grasslands. Within metapopulations, both habitat types can overlap. A critical factor for the butterfly’s presence is an adequate abundance of host plants.
Since the Marsh Fritillary requires a warm microclimate for larval development and the metabolism of secondary compounds from its host plants, it depends on open vegetation. Consequently, the species is highly dependent on the management of its habitat. Extensive grazing and single-mow management of nutrient-poor meadows have proven to be effective management regimes despite ongoing larval losses. However, even in fallow calcareous grasslands, populations can persist for many years, provided that wildlife maintains sufficient disturbance regimes.
For the long-term survival of populations in managed sites, adequate habitat size and connectivity are essential. A total habitat size of approximately 100 hectares, as calculated in a study by Bulman et al. (2007) as the minimum size for viable metapopulations, is now rarely found in today’s cultural landscapes. Such a large area is needed to buffer the often highly fluctuating population sizes. Local extinction events due to high parasitoid densities and adverse weather conditions can occur, but these can be balanced out in subsequent years if the habitats are sufficiently interconnected.
Host Plants
Diversity and Priority
In Central Europe, the dominant host plant in wet habitats is the Devil’s-bit Scabious (Succisa pratensis). In dry habitats, the preferred host plant is the Small Scabious (Scabiosa columbaria). Additionally, in both habitat types, other plants such as the Fuller’s Teasel (Dipsacus fullonum) and Field Scabious (Knautia arvensis) are also used for egg-laying. In the Bavarian Alpine foothills, where our study area is located, there are also records of additional species from the Teasel family (Dipsacaceae) and Gentian family (Gentianaceae). Above an altitude of about 1,200 meters, the Shiny Scabious (Scabiosa lucida) replaces the Small Scabious and Devil’s-bit Scabious. However, stemless gentians, such as the Clusius’ Gentian (Gentiana clusii), Koch’s Gentian (Gentiana acaulis), and Spring Gentian (Gentiana verna), can also play a significant role as host plants, especially in the spring in the harsh Alpine climate.
Threats & Conservation
Over the last century, the populations of the Marsh Fritillary have dramatically declined across Europe. The causes of endangerment begin with the direct destruction of the butterfly’s habitats, such as large-scale drainage of landscapes in Central Europe, often accompanied by the conversion of grasslands. Since the mid-20th century, the intensification of agriculture and the abandonment of traditional land use practices have also significantly contributed to the butterfly’s decline. Moreover, inappropriate habitat management, such as the use of overly heavy machinery, can negatively impact the habitat and, consequently, the populations of the Marsh Fritillary (see image). Currently, the butterfly is classified as critically endangered in Germany according to the Red List and is listed in Annex II of the Habitats Directive, which protects the species and its habitat throughout Europe. Due to its protected status and its role as an umbrella species, the Marsh Fritillary is often used as a target species in conservation projects. In Germany alone, various large-scale projects for the protection of the butterfly and its habitat have been conducted over the past two decades. Nevertheless, most populations of the Marsh Fritillary remain at critically low levels.
