Vulnerable butterfly recorded in the Botanical Garden at Uppsala

On sunny days in June, visitors to the Botanical Garden in Uppsala might spot something unexpected hovering just above the grass — a delicate flutter of tiny wings no wider than two centimeters. Researchers conducting a BioBlitz in the garden have discovered the Small Blue butterfly, Cupido minimus, thriving in one of its meadows. Around 20 of the butterflies have been observed flying low over the grass on warm, sunny days.

It is a small victory worth noting. The Small Blue is the smallest of roughly 20 blue butterfly species found in Sweden, with a wingspan of just 18 to 25 millimeters. Its underside features a band of small black dots ringed in white. Once common in Sweden's calcium-rich hay meadows, the species has suffered dramatic losses as those grasslands disappeared. Since the 1930s, Sweden has lost 80 percent of its hay meadows — a decline that has pushed the Small Blue onto the Swedish Red List as a vulnerable species.

Today, the butterfly survives primarily in scattered habitats: shingle beaches, abandoned gravel pits, and warm roadside embankments where its preferred food plant, Kidney Vetch, still grows. Female Small Blues lay their eggs in Kidney Vetch flowers, and once hatched, the caterpillars are tended by ants — a delicate partnership that depends on specific conditions.

In the Botanical Garden, researchers found the butterfly abundant in a meadow where grass is left uncut until mid-July or later. While no Kidney Vetch grows there, the meadow does offer Bird's-Foot Trefoil, Red Clover, Bush Vetch, Black Medic, and Meadow Vetchling — alternative legumes the female butterflies appear willing to use. Nearby, the Ödeenska meadow contains a few stands of Kidney Vetch, suggesting the garden's patchwork of habitats may support the species year to year.

Garden Director Anders Backlund expressed cautious optimism about the discovery. "We are, of course, delighted that this Red Listed butterfly has found its way to our meadow in particular," he said. "It shows that our work to promote biodiversity is paying off. Let's hope that we will see the Small Blue flying around here again next year, and that our meadows continue to attract a variety of other species in the future."

The future remains uncertain, given the butterfly's dependence on specific plants and habitats. But for now, Uppsala's Botanical Garden offers a rare bright spot — a place where a vulnerable species is not just surviving, but flying in numbers.