For three decades, Catalonia’s butterfly populations have declined by 40%, with observers now counting just 60 mariposas where they once saw 100, according to the Catalan Butterfly Monitoring Scheme (CBMS), a citizen-science initiative tracking diurnal butterflies since 1994. The drop mirrors broader European trends, where habitat loss and climate shifts are pushing species toward collapse—leaving abandoned meadows as their only refuge.
The CBMS’s three-decade decline: 60% fewer butterflies in Catalonia’s abandoned grasslands
The CBMS, headquartered at the Museu de Ciències Naturals de Granollers and backed by Generalitat de Catalunya and Barcelona’s Natural Parks Network, relies on 250 volunteers to monitor 240 fixed transects across Catalonia, Andorra, and the Balearic Islands. Since its launch in 1994—inspired by British biologist Ernest Pollard’s 1970s methodology—the scheme has logged over 3 million butterflies, documenting 190 species in its three-decade span.
Yet the numbers tell a stark story. “Where we used to find 100 butterflies, now there are 60,” explains Constantí Stefanescu, the scheme’s scientific coordinator. The decline is most severe in prados y herbazales abandonados—abandoned grasslands and meadows—where butterflies depend on dwindling patches of wildflowers and shrubs like madroño (Arbutus unedo). These habitats, once common, have been overtaken by urbanization, agriculture, and climate-driven shifts in vegetation.
The CBMS’s expansion—from 11 monitoring stations in 1994 to 240 today—has improved data coverage, but the trends remain grim. “The loss of these habitats is directly tied to the collapse of butterfly populations,” Stefanescu notes. A 2023 study in the Journal of Insect Conservation found that European butterfly populations have dropped 11% in 25 years, with some regions like Belgium seeing declines of 75–100% and others like Ireland holding steady at 0–25%. The CBMS’s data aligns with these findings, though Catalonia’s 40% drop is among the steepest recorded in Spain.
Barcelona’s urban butterfly hotspots: the 52 species thriving in parks—and why they’re still at risk
While rural areas suffer, cities like Barcelona offer a microcosm of the crisis—and a glimmer of hope. The city’s Observatorio Ciudadano de Mariposas Urbanas (uBMS), launched in 2018 by the CREAF research center and Barcelona’s Parks and Gardens Institute, has identified 52 butterfly species in urban parks, up from 51 before the discovery of the cejirrubia (Callophrys avis) in 2026. This species, spotted in Parque del Laberint d’Horta, is univoltine—meaning it flies only from March to May—and relies on madroño and roldón (Coriaria myrtifolia) plants, both now rare in urban settings.
Barcelona’s 26% share of Catalonia’s butterfly diversity underscores how even small green spaces can act as lifelines. Yet the city’s 40 volunteers, who conduct weekly censuses in 29 parks, face the same pressures as rural monitors: habitat fragmentation, pesticide use, and climate change. “Mariposas diurnas are excellent bioindicators,” says a CREAF spokesperson. “Their sensitivity to vegetation changes, climate shifts, and urban pollution makes them a critical barometer for biodiversity health.”
The uBMS also participates in the CBMS, with two transects in Montjuïc and Carmel, linking urban and rural data. But the city’s 52 species—while a success story—represent just a fraction of what once thrived. “The real question is whether these populations can persist as habitats shrink,” warns Stefanescu. “Abandoned fields are their last stronghold, but even those are disappearing.”
Why Catalonia’s butterflies are disappearing—and what their collapse means for Europe’s ecosystems
The CBMS and uBMS data reflect a continent-wide crisis. A 2023 European Commission report (CORDIS) highlighted how butterfly declines mirror habitat loss and biodiversity collapse, with 71 of 576 studied species classified as threatened.
- Agricultural intensification: Humedales (wetlands)—critical for species like the Charaxes jasius (madroño butterfly)—have been drained or converted to farmland, particularly in Eastern Europe.
- Climate migration: Warmer temperatures are pushing butterflies northward, but cooler habitats are also shrinking.
- Urban sprawl: Prados abandonados—once common in Catalonia—are being paved over or left to degrade without management.
The CBMS’s 190 species include Charaxes jasius, Catalonia’s largest butterfly, whose populations are highly vulnerable to habitat loss. “When these meadows disappear, the butterflies have nowhere to go,” says Andreu Ubach, the scheme’s co-technical coordinator. “We’re not just losing butterflies—we’re losing an entire ecosystem.”
Restoring Catalonia’s butterfly populations: the four urgent actions scientists and policymakers must take
The decline has spurred action. The European Union’s biodiversity targets, though missed in 2010, remain a benchmark, and initiatives like agro-environmental schemes—which incentivize farmers to preserve wildflower strips—have shown limited success.
- Restoring abandoned grasslands: Reintroducing madroño, roldón, and wildflowers in degraded areas could revive butterfly populations.
- Pesticide bans: Many butterfly species are larval-stage dependent on specific plants—pesticides kill both the host plants and the caterpillars.
- Citizen-science expansion: The CBMS’s 250 volunteers are a model, but scaling up could provide early warnings for policy shifts.
- Climate-adaptive corridors: Connecting fragmented habitats could help species migrate as temperatures rise.
“The good news is that butterflies respond quickly to habitat improvements,” says Stefanescu. “The bad news is that we’re running out of time to implement them.”
As of June 1, 2026, the CBMS’s 30th anniversary marks a turning point. The scheme’s 3 million logged butterflies and 190 species paint a picture of resilience, but the 40% decline is a warning. Prados y herbazales abandonados—once overlooked—are now critical conservation zones. Whether they can stem the tide depends on policy, public engagement, and ecological restoration.
One thing is certain: the fate of Catalonia’s butterflies is a test case for Europe’s biodiversity. “If we lose them, we lose the canary in the coal mine,” says Ubach. “And the mine is burning.”