The Marsh Fritillary butterfly was once common across the UK and Ireland. In recent decades, it became one of the most threatened butterflies in Europe.
Now, in parts of Northern Ireland, this fragile species is finally showing signs of recovery.
Recent surveys found big increases in caterpillar nests at several sites.
This success did not happen by chance. It is the result of warmer weather, careful habitat management, and years of work by farmers and conservation groups.
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What Is The Marsh Fritillary Butterfly?
The Marsh Fritillary (Euphydryas aurinia) is a small butterfly with orange, brown, cream, and black patterns on its wings. It lives in damp grasslands and open, flower-rich fields.
This butterfly is special because it depends mainly on one wildflower for its survival: Devil’s-bit Scabious.
The female lays her eggs on this plant. The caterpillars eat its leaves.
If this plant is not present, the butterfly struggles to survive.
Over the last century, changes in farming destroyed or damaged many of the damp, rough grasslands the butterfly needs.
Fields were drained, ploughed, fertilized, and grazed more heavily. Wildflowers were lost, and the Marsh Fritillary declined.
How Farming Changes Nearly Wiped It Out
Across the UK and Ireland, farming became more intensive through the 20th century.
Wet meadows and boggy grasslands were seen as “waste” and were drained or improved for production.
That meant fewer:
- Wet, flower-rich pastures
- Patches of Devil’s-bit Scabious
- Rough, varied grass where butterflies could lay eggs and shelter
Between 1985 and 2019, the Marsh Fritillary’s distribution fell by around 43%.
More broadly, about 80% of UK butterfly species have declined in abundance or range since the 1970s.
You can see long-term data on butterfly trends on the UK Butterfly Monitoring Scheme website.
The Marsh Fritillary became a symbol of how fast a species can vanish when its habitat is lost.
A Simple, Risky Life Cycle
The Marsh Fritillary has a one-year life cycle and only one brood each year.
This makes it very sensitive to bad weather or habitat loss.
The female lays clusters of eggs on the leaves of Devil’s-bit Scabious. When the eggs hatch, the small caterpillars stay together.
They spin a thin silk web around their food plant and feed inside this shared shelter.
When they have eaten that plant, they move on and build another web.
In autumn, they form a thicker silk nest called a hibernaculum. Here, they hibernate through winter.
In spring, they wake up, feed again, then turn into pupae. After a short time, adult butterflies emerge, mate, and lay eggs, and the cycle starts again.
Because there is only one generation a year, one bad season can cause a steep drop in numbers. A cold spring, a very wet summer, or sudden loss of food plants in that single year can hit the population hard.
Warm Weather Helped, But Habitat Saved The Day
Recent warm weather in Northern Ireland has helped the Marsh Fritillary.
Warm conditions improved survival for both caterpillars and adult butterflies.
But experts point out that weather alone cannot reverse decades of decline.
Climate change may bring some good years, but it also brings heavy rain, storms, and heat waves. These swings can damage nests and kill plants.
The real success factor here is habitat restoration.
The charity Butterfly Conservation has worked with farmers across Northern Ireland for years. Conservation staff and volunteers help farmers:
- Decide how and when to graze cattle
- Keep parts of fields at the right grass height
- Protect and encourage Devil’s-bit Scabious
- Maintain wet, rough grasslands that suit the species
By managing land with the butterfly in mind, farmers are turning their fields into safe, productive habitats.
The BBC’s report on this success gives more detail on these efforts: Good weather gives butterfly species a bumper year.
Counting Caterpillar Nests: How Scientists Measure Recovery
One of the most effective ways to measure the Marsh Fritillary’s recovery is to count caterpillar nests, also called larval webs.
In autumn, volunteers walk key sites and look for these silken webs on Devil’s-bit Scabious. Each web can hold anywhere from about 20 to 100 caterpillars. The number of webs gives a clear picture of how the population is doing.
The latest counts in Northern Ireland are very promising. At one site, the number of nests increased from 24 to 53 in just one year. At another, the count jumped from 24 to 139. A third site saw numbers rise from 5 to 27 nests.
These gains show that years of steady work are starting to pay off. They also prove that when habitat is restored, rare insects can bounce back.
Why This Northern Ireland Story Matters For Nature Everywhere
The story of the Marsh Fritillary in Northern Ireland is more than a local success. It is a model for how to protect other threatened species.
It shows that:
- Long-term habitat management works
- Farmers can be powerful partners in conservation
- Careful monitoring lets us see real progress, not just guess
By protecting plants like Devil’s-bit Scabious, and by allowing more natural, varied grasslands, we support not just butterflies but also bees, birds, and many other forms of wildlife.
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