A Hovering Happy Face

One of the delights of the Fall season is that Paddle-tailed Darners are out in numbers. They can be seen patrolling the shoreline of lakes, ponds, and ditches. They also hover frequently, as they keep a close watch on their territory. Here's an example of the hovering behavior:

These dragonflies are beautiful, elegant fliers.

When hovering, they flap their wings out of phase—but not 180˚ out of phase. Recall that 180˚ out of phase means that the wings are moving in opposite directions—one goes down when the other goes up. What is observed in this video, however, is a phase difference between the wings of 100˚. With this phase difference, the wings flap in such a way that when one is at it's maximum downward position, the other is at its horizontal location.

For a specific example, when the hindwings flap downward, the forewings follow a short time later, so that when the hindwings are at the bottom of their stroke, the forewings are at the horizontal position on their way down. When the forewings are at their maximum down position, the hindwings are horizontal on their way up. Flapping out of phase like this improves efficiency, allowing for minimum energy expenditure as they hover.

In contrast, when dragonflies want to accelerate and reach maximum speed they flap their wings together. This is less efficient, and hence requires more energy, but the tradeoff is worth it when the desire is to get moving quickly to chase a rival or a potential mate.