Science Focus - the home of BBC Science Focus Magazine

How can a bluebottle fly fast into a window without damage?

Subscribe to BBC Science Focus Magazine and get 6 issues for just £9.99

Bluebottle flies are speedy for their size but it's this small mass that saves them from sustaining too much damage.

Asked by: Chris Kirk, by email


Bluebottles fly quite fast for their size, but in absolute terms the speed is only around 11km/h – slower than a honeybee and much slower than most birds. But the main thing that protects them from damage is their very low mass. Kinetic energy is equal to half the mass times the velocity squared. For a fly that weighs less than 100mg, this comes to less than half a millijoule of energy. This is the same as the energy an adult man would have at a practically immobile speed of 3mm per second.


Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.


luis villazon
Luis VillazonQ&A expert

Luis trained as a zoologist, but now works as a science and technology educator. In his spare time he builds 3D-printed robots, in the hope that he will be spared when the revolution inevitably comes.


Sponsored content