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Three main factors limit the altitude that winged insects can reach: air density, temperature and oxygen availability. All three relate to the fact that Earth\u2019s gravitational pull<\/a> gets weaker the higher we rise above sea level, allowing air molecules to spread out. The fewer molecules a given volume of air contains, the \u2018thinner\u2019 \u2013 or less dense \u2013 it becomes.<\/p>\n Flying grows increasingly challenging as air density decreases because there are fewer molecules for an insect\u2019s wings to push against. Insects need oxygen<\/a> to survive just like we do, but by 6km up, oxygen levels fall<\/a> below 50 per cent of sea level values, making it harder to maintain wing flapping.<\/p>\n Finally, fewer molecules mean less heat generated by molecules bumping into one another. Temperature varies in complex ways with altitude, and some layers of the atmosphere<\/a> are warmer than others, but between Earth and about 10km up, the temperature steadily drops to less than -50\u00b0C.<\/p>\n Despite these hurdles, some insects have developed strategies that allow them to fly at high altitudes. In 2014, scientists found that alpine bumblebees living 3.25km<\/a> above sea level use different flight mechanics at higher elevations, moving their wings in a wider arc to stay aloft in thin air.<\/p>\n In the lab, the bees could even fly in chambers that simulated air density and oxygen levels at 9km \u2013 higher than Mount Everest! In reality, the temperatures at such altitudes would shut down the flying muscles of bees.<\/p>\n Read more:<\/strong><\/p>\n