Climate warming may cause Meadow Brown butterflies to lose spots

In a study conducted by scientists at the University of Exeter, it has been discovered that female Meadow Brown butterflies are experiencing a decline in the number of spots they possess as a result of warmer weather conditions caused by climate change.

Traditionally, these butterflies have been known to exhibit varying numbers of spots, with large ‘eyespots’ adorning their forewings, believed to startle potential predators. Additionally, smaller spots on their hindwings have been thought to aid in camouflage when the butterflies are at rest.

However, the recent findings challenge this long-standing belief. It appears that female Meadow Browns, which develop under 15°C, have, on average, only three spots compared to the six spots seen in those developing under 11°C.

“Our research demonstrates that the number of hindwing spots decreases when female butterflies experience higher temperatures during their pupal stage,” explains Professor Richard ffrench-Constant from the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall. “This suggests that the butterflies adapt their camouflage based on environmental conditions.”

The implications of this discovery are significant. With fewer spots, the Meadow Browns may become more difficult to detect on dry, brown grass that is more prevalent during hot weather. In essence, they are adjusting their camouflage strategy to match the changing environment.

Interestingly, the research did not observe a similar effect in male Meadow Browns. This discrepancy could be attributed to the importance of spots in attracting mates, known as sexual selection.

The Meadow Brown butterfly has long been regarded as an example of “genetic polymorphism,” a phenomenon where multiple genetic forms coexist within a single population. However, this study highlights that the variation in spots is not solely due to genetics but is, in fact, a result of thermal plasticity, the ability to respond to temperature changes.

For Professor ffrench-Constant, this study holds personal significance. “This research is particularly meaningful to me as my father collected butterflies for EB Ford, right here in Cornwall,” he shares.

To conduct the study, researchers examined both current populations of Meadow Browns in Cornwall and historical collections from Eton and Buckingham. Through meticulous daily observations throughout the flight season, they were able to gather invaluable data on spotting patterns.

The implications of this research extend beyond the Meadow Brown butterfly. As our climate continues to warm, the researchers predict that spotting in this species will progressively decrease year after year. This unexpected consequence of climate change challenges our typical understanding of species’ responses, which often focuses on their migration towards cooler regions.

Meadow Browns typically spend approximately 28 days in the pupal stage, with emergence occurring in late spring within the United Kingdom.