The Balearic Marbled Skipper (Gegenes pumilio), one of Europe's most endangered butterflies, has found its last sanctuary in the Balearic Islands. Recently added to Spain's Red List of Threatened Species, this African migrant species has been spotted in select locations across Mallorca, including Raixa, Soller's Jardí d'en Perelló, and es Comú de Muro.
"Historically abundant in Mallorca, it's now extremely rare, which led to its recent classification as endangered in Spain," explains Dr Pau Colom, researcher at Imedea Uib-Csic and coordinator of the Catalan Butterfly Monitoring Scheme (CBMS). The species' similarity to the Mediterranean Skipper has prompted Balearic lepidopterists to conduct genetic analysis to confirm local sightings.
On 15th May, the Balearic Museum of Natural Sciences reported a significant sighting by amateur entomologist Cristian Rodríguez, who observed the butterfly feeding on flowers near the insect hotel in the botanical garden.
Butterflies serve as essential bioindicators due to their ectothermic nature, with body temperatures dependent on external conditions. Population counts have become crucial in measuring global warming effects, as these insects' biological cycles are intrinsically linked to climate patterns.
The CBMS monitoring network has grown to include 21 routes across the Balearic Islands: 12 in Mallorca, 7 in Menorca, and 1 each in Ibiza and Formentera. "Butterfly populations in the Balearics, part of CBMS's arid region network, often show different dynamics compared to mainland populations," notes Dr Colom.
Long-term data shows declining numbers of sedentary species like Southern Gatekeeper and Southern Brown Argus. However, migratory and generalist species such as Lang's Short-tailed Blue and Painted Lady have shown population increases over the past decade.
A notable development is the expansion of Danaus genus butterflies. Between 2023 and 2024, the Monarch butterfly was recorded in six Mallorcan routes, while the Plain Tiger appeared in five Mallorcan and three Menorcan locations. Both species are closely associated with the naturalised tropical plant Gomphocarpus fruticosus.
"Future challenges include consolidating long-term monitoring of existing routes and expanding coverage, particularly in the Pityusic Islands and areas where rare species persist," states Dr Colom. The project aims to better represent understudied populations, including the Wood White, Cardinal, and the endangered Balearic Marbled Skipper.