Why don't butterflies fly in straight lines?

The butterfly’s erratic flight is actually an evolutionary tactic that makes it harder for any would-be predators to predict the insect’s flightpath.

19th November 2014

Asked by: Jamie Fitzpatrick, Dublin

Butterflies and moths use their wings for many purposes: for flight, as mobile billboards to advertise how poisonous they are, and to create camouflage patterns. So you would expect them to be less adept fliers than insects that have optimised their wing design purely for aerodynamics. But the butterfly’s erratic flight is actually an evolutionary tactic that makes it harder for any would-be predators to predict the insect’s flightpath. The more poisonous butterflies don’t need to carry out these evasive manoeuvres, and as a result these species tend to fly much straighter.

Fluid dynamics simulations that were carried out at Kyoto University in Japan last year showed that butterflies achieve their trademark swoops and tumbles by generating a lot of extra turbulence with each wing beat. And high-speed photography studies undertaken at Johns Hopkins University in Baltimore, US, reveal that they also constantly adjust their centre of gravity by shifting the position of their body and wings.

Monarch butterflies are so good at this that they can effect a 90-degree turn in less than a single body-length.