Bielsa, Spain – Every fall, an astounding migration occurs in the Pyrenees, a mountain range that straddles the border between France and Spain. Thousands of marmalade hoverflies, adorned with citrus-colored bodies and black stripes, swarm through the picturesque Bujaruelo Pass. The insects, along with white and yellow butterflies, brave harsh winds as they journey south for the winter. This mesmerizing spectacle, first documented in 1950, continues to captivate researchers like Will Hawkes from the Swiss Ornithological Institute.
The hoverflies, butterflies, and numerous other insects navigate through the pass, seeking refuge in the warmer climates of Spain or even journeying as far as Sub-Saharan Africa. Situated at almost 7,500 feet above sea level but less than 100 feet wide, the Bujaruelo Pass acts as a vital gateway for these tiny creatures. Despite the challenging conditions, with scant vegetation and frigid nights, the insects press on, driven by a steadfast determination that is evident in the incessant buzzing that fills the air.
In an effort to shed light on this extraordinary migration, Hawkes and a team of researchers embarked on a thorough survey spanning four years. Their study, recently published in the journal “Proceedings of the Royal Society B,” utilized innovative methods to quantify the vast number and diverse species of insects passing through the pass. From meticulous hand counting of butterflies to deploying smartphone cameras to capture the influx of flies, the researchers left no stone unturned in their quest to understand this phenomenon.
One of the most challenging aspects of their study was extracting data from the videos captured by the smartphones. Despite attempts to develop automated tools, Hawkes spent weeks painstakingly counting individual flies in the footage. The researchers also set up net traps to collect a representative sample of the migrating insects, providing valuable insights into the composition of this bustling ecosystem.
Through their analysis, the researchers estimated that a staggering 17.1 million insects traverse the Bujaruelo Pass annually, highlighting the critical role this mountain pass plays in facilitating these migrations. Notably, hoverflies emerged as the predominant flyers, comprising 90% of the recorded insects. This revelation underscores the significant ecological impact of these unassuming pollinators, whose importance often goes unnoticed in traditional pollinator research focused predominantly on bees.
As concerns mount over declining insect populations worldwide, Hawkes emphasizes the urgency of conservation efforts to safeguard these vital species. Habitat loss, pesticide use, and climate change pose significant threats to hoverflies and other insects, highlighting the need for proactive measures to protect these essential pollinators. By fostering a deeper understanding and appreciation for these remarkable migrants, Hawkes hopes to inspire action to create a more hospitable environment for these crucial contributors to our ecosystem. He emphasizes the resilience of insects like marmalade hoverflies, urging communities to take steps to preserve their habitats and ensure their continued survival and proliferation.