The Fate of the Glimmering Butterfly: A Disappearing Species

In July 2019, on the border between Kalmar and Östergötland counties, a shimmering female butterfly searches for a suitable leaf of the sweet vernal grass to lay her eggs. This plant is essential, as its leaves are the sole food source for her larvae.

Despite occasional rain showers, the ground remains parched from the persistent drought of the previous summer. Many plants appear stressed and sparse. The female inspects each sweet vernal grass plant, characterized by its distinctive pods, but finds only a few scattered healthy leaves. Once abundant in the area, the sweet vernal grass has diminished since the land ceased to be grazed by sheep, allowing bushes and undergrowth to dominate. The location has become shadier and overgrown.

She lands on a small, faded leaf, scrapes it with her front legs, and smells it with her antennas. It may not be ideal, but she feels an urgency to lay her eggs.

This scenario paints a picture of what might be the last surviving individual of the butterfly species known as the Common Blue. The species was last sighted in Sweden in the summer of 2019, and despite extensive searches, it has not been found since. The extreme drought of the summer of 2018 likely contributed to the decline of both the Common Blue and another butterfly species, the Veronica Butterfly, which are now feared to be extinct in Sweden.

Both species were already rare before 2018, but the drought may have sealed their fate, according to environmental analysis experts.

The decline of these butterflies reflects a broader global issue. A recent study published in Science indicates that the number of butterflies in the United States has decreased by 22 percent over just two decades. This rapid decline is alarming, showing significant reductions across various species, including common butterflies.

Fact: The Butterfly Crisis in the U.S.

• From 2000 to 2020, butterfly populations decreased by 22 percent.
• The number of declining butterfly species is 13 times greater than those that are increasing.
• Many species have seen dramatic declines: 107 species have decreased by more than 50 percent, with 22 species dropping by over 90 percent.
• The sharpest declines are in the southern regions and the southwest, where the landscape is already arid, and climate change has resulted in rapid warming.
• The study, titled "Rapid butterfly declines across the United States during the 21st century," is the most comprehensive analysis of butterfly populations in the U.S., based on 12.6 million butterflies collected from 76,000 surveys across 35 monitoring programs.

While the study did not explore the specific reasons behind the butterfly population decline, researchers identified three likely factors: habitat loss, climate change, and pesticide use in agriculture.

For years, entomologists have warned about a precipitous decline in global insect populations, although there is some disagreement on the extent of this decrease. Some studies rely on trapping methods, which can complicate assessments of population changes, while others use more targeted data from specific ecosystems. However, butterflies are among the easiest insects to monitor, as researchers can count them along established routes and record their sightings within a defined distance.

The findings from the U.S. study corroborate trends observed in Europe and Sweden over recent years. Data from Sweden's butterfly monitoring program reveals a swift decline in butterfly populations since monitoring began in 2010. For the 81 species where trends can be assessed, the median population size has dropped by 20 percent by 2024.

Moreover, the European environmental indicator for grassland butterflies has declined by nearly 30 percent between 1991 and 2020, with significant declines recorded prior to 1991.

Fact: Environmental Indicators for Grassland Butterflies

• The European environmental indicator for grassland butterflies tracks population changes among 17 species typical to grasslands.
• This indicator, which is based on data from 18 EU countries, aims to measure progress towards EU biodiversity goals and the UN's global sustainable development targets.
• Butterflies respond quickly to habitat changes, making them valuable indicators of environmental health.

A decrease in butterfly populations signals a loss or degradation of their habitats. Butterflies are crucial indicators of environmental conditions and biodiversity, reflecting the landscape and the habitats available to them.

Most butterflies thrive in varied and flower-rich agricultural landscapes, where traditional practices such as mowing or grazing are employed. However, intensified and large-scale agricultural and forestry practices have led to fewer habitats where butterflies can find food and host plants, such as meadows, hedgerows, roadside ditches, and open forest edges.

As open fields dominated by a single crop or conifer plantations are not conducive to butterflies, the loss of previously open and flower-rich areas is a significant challenge for these insects.

Despite the negative trends, there are successful conservation efforts underway. Initiatives like the "Butterfly Landscape" along the border of Jämtland and Medelpad are examples of successful conservation efforts that support a range of rare and endangered butterflies.

To assist butterflies, local authorities in Västernorrland and Jämtland have collaborated with various stakeholders to implement measures such as mowing, clearing, and managing roadside vegetation. These efforts have not only benefited butterflies but also birds, flowers, and other insects in the region.

Through collaborative efforts and dialogue with land users, sustainable solutions are being developed that benefit both the agricultural sector and butterfly populations.