A Himalayan butterfly named Golden Birdwing is India’s largest, a record an unknown specimen had held for 88 years.

With a wingspan of 194 mm, the female of the species is marginally larger than the Southern Birdwing (190 mm) that Brigadier William Harry Evans, a British military officer and lepidopterist, had recorded in 1932. But the male Golden Birdwing (Troides aeacus) is much smaller at 106 mm.

While the female Golden Birdwing was recorded from Didihat in Uttarakhand, the largest male was from the Wankhar Butterfly Museum in Meghalaya capital Shillong.

According to the authors, the only measurement used in the study of Lepidoptera is wingspan — a simple concept with various interpretations of the term.

Brigadier Evans followed a more reliable method. He measured a butterfly from the centre of the thorax to the tip of the forewing apex and doubled the result. He provided wingspans of all butterfly species then known from the Indian subcontinent and his book is still the standard work on the subject.

The updated wingspan of three species — all from Uttarakhand — after the Golden Birdwing are Common Windmill (Byasa polyeuctes) at 98 mm, Great Windmill (Byasa dasarada) at 96 mm, and Common Peacock (Papilio bianor) at 78 mm.

The smallest is the Quaker (Neopithecops zalmora) with a wingspan of 18 mm and forewing length of 8 mm. The largest female Golden Birdwing’s forewing length is 90 mm.