Highest migrating butterfly

The highest butterfly migration reliably recorded was that of a small flock of small tortoiseshells (Aglais urticae). It was seen flying over the saddle of the Zemu Glacier in Sikkim, a north-eastern Indian state in the eastern Himalayas, at a height of 19,000 feet (5,791 metres), as documented by English entomologist C B Williams in a book published in 1958. There have also being reports of Queen of Spain fritillaries (Issoria lathonia) flying in the Himalayas at a height of approximately 6,000 metres (19,685 feet), but these latter reports are currently unverified; the normal maximum flight altitude of this species is around 2,700 metres (8,860 feet).

This is, in fact, the highest that any insect has been observed in controlled flight (lightweight insects such as aphids sometimes get carried by air currents to even higher altitudes but this is outside of their control.) In comparison, the highest altitude recorded for a bird is 11,300 m (37,000 ft) for a Rüppell's vulture (Gyps rueppellii), which collided with a commercial aircraft over Abidjan, Ivory Coast, on 29 November 1973.

The monarch (milkweed) butterfly (Danaus plexippus) is famed for the record-breaking distances undertaken during its spectacular mass migrations (circa 4,800 km/3,000 mi), but it is also quite a high-flyer, in the literal sense. During one autumn migration of monarchs, a glider pilot encountered one specimen at a height of 11,000 ft (3,353 m).