Barcelona has identified a new butterfly species, the Rosy Green Hairstreak ( Callophrys avis ), for the first time. The discovery, made a few weeks ago at Parc del Laberint d'Horta, brings the city's total number of recorded diurnal butterfly species to 52, representing approximately 26% of all species found in Catalonia, according to Barcelona City Council.
The Rosy Green Hairstreak is a univoltine species, meaning it has only one generation per year, flying exclusively from March to May. This specialist butterfly relies heavily on the presence of two specific plants: the strawberry tree (Arbutus unedo) and the myrtle-leaved coriaria (Coriaria myrtifolia).
Diurnal butterflies, including the Rosy Green Hairstreak, are considered excellent bioindicators of environmental quality. Their sensitivity to changes in vegetation, climate, and ecological conditions provides valuable information about the state of urban biodiversity. In their larval stage, these species depend exclusively on a limited number of plants. If these plants disappear or decrease, butterfly populations also decline rapidly. Butterflies also respond sensitively to the effects of climate change.
Beyond their ecological value, butterflies play a fundamental role in urban ecosystems as primary consumers and as a food source for numerous predators and parasitoids. They also help connect citizens with urban nature due to their easy identification and high educational and aesthetic appeal.
Volunteer Efforts Drive Discovery
The discovery was made possible by the volunteer network of the urban Butterfly Monitoring Scheme (uBMS), a project coordinated by the Ecological and Forestry Applications Research Centre (CREAF). This scheme has operated in Barcelona since 2018, under an agreement with the Barcelona Municipal Institute of Parks and Gardens. Currently, nearly 40 volunteers actively participate in weekly butterfly monitoring across 29 city parks and gardens.
Between March and November, volunteers conduct visual censuses to collect data on the presence and abundance of different species. In addition to the uBMS monitoring, Barcelona also participates in the Catalan Butterfly Monitoring Scheme (CBMS), promoted by the Granollers Museum of Natural Sciences, which conducts monitoring along two routes in Montjuïc and Carmel.
The main goal of these butterfly monitoring programmes is to gather long-term data on species presence and abundance. This helps understand the diversity of species in the city, analyse population trends, identify urban factors that help or limit biodiversity, develop ecological management tools, and create indicators of urban biodiversity quality.
Impact of Climate and Management
Accumulated data shows that despite an increase in the number of detected species, the five most common species currently account for 64% of all observations. This pattern indicates a community primarily composed of generalist species better adapted to urban environments.
Barcelona is implementing various naturalisation strategies to support species with more specific ecological requirements. Key actions include establishing urban meadows and grasslands, low-intensity forest management in natural areas such as Montjuïc, the Tres Turons, Collserola, or the Rec Comtal, and creating biodiversity refuges. These measures aim to improve ecological connectivity, increase habitat quality, and balance the abundances of different species in the city.
Monitoring data has also shown the direct impact of climatic and management factors on butterfly populations. In 2020, coinciding with the lockdown and reduced intervention in green spaces, along with wetter weather conditions, a notable increase in butterfly abundance was recorded in the city. However, the prolonged drought between 2021 and 2023 led to a significant decrease in observed populations. Data from 2024 shows a progressive recovery.
Individuals interested in butterflies who wish to join the uBMS volunteer network can find all information on the project's website.
