Amateur Finds Rare Butterfly, Creates New Survey Method

When Gareth Tilley spotted an unusual butterfly during a 2020 lockdown walk near his Epsom home, he had no idea he was about to revolutionize how scientists track endangered species.

The amateur butterfly enthusiast had just discovered a black hairstreak, one of Britain's most elusive butterflies, in Surrey for the very first time. Before that moment, scientists believed this rare species lived exclusively in woodlands between Oxford and Peterborough, over 60 miles away.

Some locals thought someone must have illegally released the butterfly. But Tilley knew what he'd seen mattered, so he teamed up with Butterfly Conservation, the local council, and the University of Sussex to prove a wild population truly existed in Surrey.

The challenge was finding proof. Black hairstreak caterpillars look exactly like leaves, their chrysalis resembles bird droppings, and adult butterflies stay hidden high in tree canopies, making them notoriously difficult to track.

Then Tilley learned about an intriguing phenomenon: some caterpillars in the United States glow under UV light. In May 2022, he bought a UV torch and headed out into the Surrey woods, skeptical but curious.

"When I found a caterpillar, it didn't just glow, it was incredibly bright," Tilley said. In just one evening, he found 46 caterpillars, more than researchers typically find in entire seasons using traditional methods.

Scientists still don't know why these caterpillars glow. It might help deter predators, or it might serve no direct function at all, but the mystery doesn't diminish the discovery's impact.

The Ripple Effect

Butterfly Conservation immediately recognized the game-changing potential of Tilley's technique. The charity now promotes UV surveying for hairstreaks across the entire United Kingdom, and the method is revealing butterfly populations scientists never knew existed.

Steven Lofting, the charity's southeast conservation manager, says the work has made a "hugely valuable contribution" to butterfly conservation. Teams are finding much higher numbers of hairstreaks using UV surveys, and the fun, accessible approach is attracting more volunteers to conservation work.

The technique is spreading beyond British borders too. Tilley is now sharing his method with conservation groups in Australia, where scientists hope it will help them monitor their own threatened butterfly species.

The timing couldn't be better: black hairstreak populations have declined 33% since 2002, largely due to habitat loss. What started as one curious person's lockdown hobby has become a powerful new tool in the fight to save vulnerable species worldwide.