#322 Why do dragonflies have four wings?

Why do dragonflies have four wings? So that they can hover and fly in any direction that they wish.

Most insects have two pairs of wings but the second set in some of them have evolved to have a different purpose. Two examples of these are flies and beetles. (I know we are talking about dragonflies, but they are not actually flies.)  Flies used to have four wings, but the second set of wings evolved into halteres. These are gyroscopic organs that oscillate in time with the wings and give the fly excellent balance and maneuverability. Beetles also used to have two sets of wings, but the first set evolved into the hard cases that cover the wings when they are folded away. These are called elytra and the beetles have to open them so that they can fly.

Insects use their wings to fly in two different ways. There is direct flight and indirect flight. Direct flight is where the flying muscles attach to a hinge at the base of the wing. They flap the wing by contracting and pulling on this hinge. Insects that fly with direct flight can only flap their wings as fast as they can send signals to their muscles. Dragonflies use the direct flight method to fly. They cannot flap as fast as the indirect flight method, but insects that use the direct flight method have the ability to move their wings independently.

Indirect flight is where the flying muscles don’t connect to the wings directly. They attach to the walls of the thorax. When the insect wants to fly, the muscles pull on the thorax and change its shape. The wings are attached to the thorax and when it is warped by the muscles, the wings move up. There are four muscles attached to the thorax. The muscles that raise the wings are attached to the top and the bottom of the thorax and the muscles that lower the wings are attached to the front and the back of the thorax. While one is stretched, the other is relaxed and vice versa. The muscles are activated automatically by being stretched. When one set of muscles pull the wings down, that stretches the other set of muscles, which activate and start to pull the wing back up. This process repeats. Because the muscles are activated automatically, it means the insect doesn’t have to send a signal from its brain, so indirect flight insects can flap their wings much faster than direct flight insects. For example, a midge can flap its wings at over 1000 times a second.

So, why do dragonflies have four wings? Dragonflies have four wings because that is the most common number of wings for an insect. The wings on insects that use indirect flight are usually fused into one wing, but they are still technically two wings. A better question is, how do dragonflies use their four wings?

The muscles that move a dragonfly’s wings are connected to the hinges at the bottom of its wings. This means they can only flap their wings about 30 times a second. This is about twice as fast as a hummingbird. However, because their muscles are connected to each wing, they can move their wings independently, in the same way that we can move our arms independently. This allows them to turn extremely quickly, and it also allows them to hover. Most insects that use direct flight are unable to hover, but dragonflies can because they are able to turn their wings independently and even flap them out of sync. When dragonflies take off, they flap all of their wings at the same time to gain maximum lift, but when they are hovering, they flap them out of sync, so the front wings are flapping up while the back wings are flapping down. This means they can hover perfectly motionlessly, and it also means they use less energy when they fly.

Dragonflies prey on small insects such as mosquitoes and midges. Don’t be upset if you see lots of dragonflies because they are eating the mosquitoes that make our lives hell. Because mosquitoes can fly so quickly, dragonflies have to be able to maneuver quickly to catch them, which is why they have evolved their flight system. However, their amazing wings come with two drawbacks. The first is that they cannot furl their wings to protect them. Many insects can fold their wings or hide them inside a hard shell. Dragonflies cannot do this. Their wings harden after they change from larvae to dragonflies, and they cannot be folded. This means they are broken easily. Secondly, there are four sets of muscles moving the wings, so dragonflies need to eat more food than other insects. They have to consume about 20% of their body weight every day, which is one reason why they spend a lot of their time just sitting on something.

So, why do dragonflies have four wings? So that they can maneuver quickly to catch insects.

Photo by Pixabay: https://www.pexels.com/photo/red-dragonfly-on-brown-twig-66264/

Sources

https://en.wikipedia.org/wiki/Beetle

https://en.wikipedia.org/wiki/Fly

https://biology.stackexchange.com/questions/92614/why-are-two-winged-animals-much-more-common-than-four-winged

https://meadowia.com/why-and-how-does-a-dragonfly-fly/

https://www.smithsonianmag.com/science-nature/14-fun-facts-about-dragonflies-96882693/

https://www.sciencedaily.com/releases/2014/11/141124074735.htm

https://www.ck12.org/c/biology/insect-flight/lesson/Insect-Flight-Advanced-BIO-ADV/

https://www.si.edu/spotlight/buginfo/insect-flight

https://dragonflywebsite.com/dragonfly-flight.cfm

https://asknature.org/strategy/wing-structure-allows-rapid-acceleration/