My 4-year-old daughter asked me how high butterflies fly. I was stumped. Can anyone tell us?
鈥� Unlike humans, butterflies are not disposed to seeking altitude records. Indeed, they will not fly higher than is strictly necessary in their everyday lives, whether looking for a mate, food, somewhere to lay eggs, avoiding predators or migrating.
Worldwide there are many thousands of species of butterfly, each adapted to its own particular habitat and needs. Some spend their whole lives on a patch of coastal grassland, the larvae feeding on low plants or living in ants鈥� nests, and the adults never flying more than a few feet above the ground. Others spend all their time in the tree canopy many metres above ground level.
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Still others are only found on high mountains. So even though they don鈥檛 actually fly very high above the ground locally, butterflies that live on the mountains of Peru spend their whole lives at altitudes of around 6000 metres.
Butterflies that migrate tend to fly the highest in general. The most famous migratory butterfly is probably the monarch, . These leave Mexico each year and fly north to Canada, albeit taking several generations to get there. Monarchs have been sighted by glider pilots flying as high as 1200 metres. Interestingly, they seem to fly in the same way as a glider, using updrafts to gain sufficient altitude so that they can glide for quite a distance before needing to use energy to climb again.
鈥淢onarch butterflies leave Mexico each year and fly to Canada, albeit taking a few generations to get there鈥�
Europe also has plenty of migratory species. The painted lady, , makes its way to southern France from north Africa. It has to leave Europe in winter as no development stage of this insect can survive a frost.
To get to France many will cross through the mountain passes of the Pyrenees, which in general lie at about 2500 metres. During late summer and autumn one can observe butterflies drifting southwards. If they encounter a high building, they just fly straight upwards and over it. If they encounter a high mountain range, they will do the same. So you need only to stand for a while on any mountain pass during the migration period to see them coming over either singly or in swarms, flying close to the ground as they travel.
The mountain passes of the Caucasus are higher, while those of the Himalayas are higher still at 7500 metres. I wouldn鈥檛 be surprised if migratory butterflies could fly straight over mount Everest if they encountered it in good weather.
However, insects of any kind cannot fly if they are too cold. Butterflies can keep warm to a certain extent by beating their wings, though if they fly too high in the wrong conditions, they may become too chilled to maintain a wingbeat.
On average, the air temperature reaches freezing at an altitude of just below 8000 metres, suggesting that this would be their physical altitude limit. They might on occasion be carried higher on updrafts, but this surely doesn鈥檛 count as autonomous flight.
Terence Hollingworth, Blagnac, France
鈥� The greatest acknowledged height achieved by migrating butterflies is 5791 metres, set by a flock of small tortoiseshells, , crossing the Zemu glacier in the eastern Himalayan mountains.
鈥淭he greatest acknowledged height achieved by a butterfly is 5791 metres, seen over the Himalayas鈥�
Not only is this an altitude record for butterflies, it is also the highest that any insect has been observed in controlled flight, comfortably exceeding the more frequent altitudes of between 3000 and 4000 metres at which monarch butterflies have been sighted by commercial airline pilots.
Hadrian Jeffs, Norwich, Norfolk, UK