Why Do Flies Fly in Circles?

In order to answer the question “Why do flies fly in circles?” we must first understand how flies move. The way that they move is crucial for their survival. They need to fly straight, not in circles, so they can find food. They also have to regulate their forward speed. Consequently, they are sometimes blown sideways by the wind. This allows them to cover the largest distance possible, increasing their chances of finding a food source.

We may not think of insects as emotional creatures, but we have a pretty good idea of how they work. As insects, flies have evolved to be highly aerobatic. In order to attract mates, they need a meeting place. For this purpose, they patrol a well-defined airspace beneath landmarks. The turning angle is sharp enough that a competing fly will avoid it, but not so sharp that it will end up flying at an angle that would make it impossible for the competing fly to get a missile lock.

The distance between flies landed and the surface they hit increased with perpendicular velocity. This is referred to as tau. When a fly makes contact with a vertical surface, its tau is relatively low, but if it makes contact with a ceiling, it will decelerate much slower than the head-contact landing.