Insect wing

Insect wings are special parts that grow out from the hard outer shell of adult insects, allowing them to fly. These wings are found on the middle and rear parts of an insect's body, called the mesothorax and metathorax. They are made stronger by lines called veins that sometimes connect to form small closed spaces, which can help scientists identify different kinds of insects.

Some insects move their wings by using muscles attached directly to the wings, while others use muscles that move the body part where the wings are attached, making the wings move indirectly. Wings are not always present in both males and females; in some insects, only one sex has wings. Also, in certain groups like ants and termites, worker insects may not have wings at all.

The way insect wings look and work has changed over time, and scientists have many ideas about how they first appeared. Some believe wings came from existing body parts, like gills or extensions of the body wall, while others think they were brand new structures that evolved just for flying. Recent studies suggest that insects share a common ancestor with crustaceans, which might explain how wings developed.

Morphology

Each wing of an insect is made of a thin membrane held up by a network of veins. These veins help keep the wing strong and stiff. The membrane is created from two thin layers that lie very close together, while the veins form where these layers are slightly apart. Inside the major veins, there are special structures called nerves and tracheae, and fluids can flow through the veins to help the wing work.

As the wing grows, the layers that form the membrane come together, leaving spaces that become the veins. The material around the veins thickens to give the wing its strength. Tiny hairs, called microtrichia, and larger hairs, called macrotrichia, can be found on the wings. Some insects, like butterflies and moths, have special scales on their wings that are changed versions of these larger hairs.

Flight

Main article: Insect flight

Insects have two main ways of flying. Some larger insects, like mayflies and dragonflies and damselflies, have muscles attached directly to their wings. These wings can only beat as fast as the nerves can tell them to move. Most other insects fly using a different method. Their muscles make the middle part of their body shake, which makes the wings beat faster than the nerves can control.

There are two main ways insects fly in terms of air movement. Most insects create a spinning flow of air along the front edge of their wings. Some very small insects bring their wings together above their body and then quickly pull them apart. When they open their wings, air is pulled in, creating a swirling flow above each wing. This helps them stay in the air, though it can wear out the wings over time.

Many insects can stay still in one place by beating their wings very fast, which needs balance as well as lifting up. A few insects can glide through the air without using force to move forward.

Main article: Insect aerodynamics

Evolution

Some time around the Carboniferous Period, about 350 million years ago, insects started to fly. We still don't fully know how or why insect wings first appeared, partly because there aren't many fossils from that time to study. There are a few main ideas about how insect wings might have developed. One idea is that wings grew from special parts of the insect's back called paranotal lobes. Another idea is that wings came from movable gills on aquatic insects like mayflies. A third idea is that wings grew from small parts of the insect's legs.

Fossils from earlier times, like the Devonian period (around 400 million years ago), show insects without wings. But by the Carboniferous period (about 320 million years ago), many insects had fully developed wings. Early winged insects included groups like Blattoptera, Caloneurodea, and Ephemeropterans. Some of these early insects had large, flat forewings with special veins.

During the Permian period, dragonflies became major flying insects. They were very successful flyers and some had very large wingspans. Other insects like early beetles also developed wings during this time.

There are several theories about how insect wings evolved:

• Paranotal hypothesis: This idea suggests wings grew from special parts on the insect's back. These parts might have helped insects slow their fall when jumping or falling. Over time, these parts grew larger and developed muscles, allowing insects to glide and eventually fly.
• Epicoxal hypothesis: This theory suggests wings came from special gills on water insects. These gills might have changed over time to help with movement and eventually became wings.
• Endite-exite hypothesis: This idea says wings developed from small parts of the insect's legs. Studies on modern insects support this idea because the muscles and joints needed for wings are already present in leg parts.
• Paranota plus leg gene recruitment hypothesis: This newer idea combines the first two theories. It suggests wings first grew from the insect's back and later changed using genes normally used for legs, allowing them to move and function better.

Wings may have first helped insects move on water or glide through the air before true flight evolved. The first flying insects were similar to modern dragonflies, with two pairs of wings and strong muscles for flying. Over time, most insects evolved to have just one pair of wings or special ways to fold their wings.

Natural selection helped improve insect wings for better flight. Many insects can twist their wings and change the shape of their wings to help them fly more efficiently. Some insects can even generate three times their body weight in lift and five times their body weight in thrust, allowing them to fly very well and escape from larger animals.

Morphogenesis

Insects that go through complete metamorphosis, like those in the Endopterygota, develop their wings during the pupal stage. However, insects with incomplete metamorphosis, such as those that are hemimetabolic, have a different way of growing wings. Their wings start as small buds under the outer layer and only appear fully in the last stage before becoming adults, called the nymph.

Very early in an insect's life, even before it hatches, we can see the first signs of wings as small thickenings under the outer skin. As the insect grows, groups of cells form under the outer layer and eventually create a pocket. In some insects like White butterflies (Pieris), these pockets grow longer and push out to become wings. By the time the insect is ready to become an adult, the wings are fully formed and ready to be used.

The wings also develop tiny tubes called tracheoles that help them get oxygen even as they are growing. These tubes stretch out to reach all parts of the wing, making sure the wing gets enough air to develop properly.

Nomenclature

Many names of insect groups come from an ancient word for wing. The word "pteron" is part of their names, showing how important wings are to these tiny creatures.

Adaptations

Insect wings are very important for telling different insect species apart. Each group of insects has its own special wing shapes and features. Even within a species, colors and patterns on the wings can help tell them apart. Most insects fold their wings when they’re not flying, but some, like dragonflies, hold their wings out flat. Others, like moths and butterflies, fold their wings upward.

The shape of an insect’s wings often matches how well it can fly. Insects that fly very well usually have long, slim wings. For example, sphinx moths have large, pointed front wings that look like the wings of modern airplanes. Strong muscles connected to the wings also help insects fly fast and well. The wings are built to handle the forces of flight, with thicker veins at the front for strength and thinner, flexible veins at the back.

Variation of the wing beat may also occur, not just amongst different species, but even among individuals at different times. In general, the frequency is dependent upon the ratio between the power of the wing muscles and the resistance of the load. Large-winged, light-bodied butterflies may have a wing beat frequency of 4–20 per second whereas small-winged, heavy-bodied flies and bees beat their wings more than 100 times a second and mosquitoes can beat up to 988–1046 times a second. The same goes for flight; though it is generally difficult to estimate the speed of insects in flight, most insects can probably fly faster in nature than they do in controlled experiments.