Flight has always intrigued and inspired human beings. Since antiquity we created stories, myths, and legends about flight, and flying is arguably one of humanity’s greatest achievements… Since flight became a reality in 1903 with the Kitty Hawk we continue to aspire better, faster and more efficient aviation, to the most recent “Flying car”. (No, not Doc Brown’s time travel car from “Back to the Future” or “Chitty Chitty Bang Bang” but a real flying car! You can reserve one here.) So it is no wonder that we are enthralled and are continuing to learn about flight from insects and birds. Insects, my “bread and butter”, were the first to evolve flight and, as such, have long since perfected the ability long before us! As usual, we may have a lot to learn insects!
An insect, is made up of three segments: head (first and, hopefully, obvious section), thorax (middle section), and abdomen (last section). Internally, the thorax is chuckfull of muscles, making it is the “engine” responsible for locomotion via legs and wings. Even though legs are intriguing and have many adaptations as well, this post focuses on insect wings, their evolution and variation. To be honest, I’ve chosen this topic to show off all the high speed videos my colleagues, Mike Hrabar and Sean McCann, have taken in the Gries lab… they are SO amazing! You will be mesmerized! I promise. (I may show some of my own soon… still holding out for possible publication.)
There are four theories regarding wing evolution, plus my Laymen explanation, (1) Paranotal process, or wings developed from projections (or bumps) on thorax, (2) Epicoxal, or wings developed from abdominal gills (i.e. mayflies and nymphs), (3) Endite-exite, or wings developed from gill branches on the leg, (4) Paranota plus leg gene recruitment, or wings developed from projections on the thorax aided by hereditary genes from legs which were transfered to the projection producing muscles needed for flight. I’ve been taught that the “paranotal process theory” is the most widely accepted, with matching fossil records from cockroach relatives that indicate the paranotal lobes were originally a mechanism that allowed the insect to glide down from treetops. However, I’m beginning to be convinced of “paranota plus leg gene recruitment theory” because it is in agreement with the fossil records and the most recent genetic studies.
SO, insects were the first to evolve flight! Having two pairs of wings, they have faced problems with drag and turbulence when their wings beet together. We face these same problems when engineering flight devices, but, unlike us, insects have evolved many ways to overcome this issue and stabilize their motion. Consequently, these adaptations are fundamental in identifying and classifying insects into groups.
Dragonflies and Damselflies have two pairs of wings that are approximately the same size and shape with many veins throughout. This group of insects has developed a reversed (or alternated) wingbeat that can clearly observed in this slow motion video (Valevids, 2010).
Similarly, this alternated wingbeat can be seen in Lacewings (Order Neuroptera).
Flies (Order Diptera) have 1 pair of large functional wings and a pair of reduced hind wings called a halteres. Although small, they have a important role in flight, and are used for orientation and balance. Look closely for the halteres in the below video of a hoverfly (Family Syrphidae), they look like tiny little drumsticks behind the first pair of wings. You can see them beet in an alternate pattern with the first and large wings.
Most beetles (Order Coleoptera) have a hardend first pair of wings, called elytra. Making only the second pair of wings functional for flight. These second pair of wings are folded longitudinally (lengthwise) and transversely (across) under the elytra. There is a spring mechanism, in addition to abdominal movements, that keep the wings folded and in place.
Butterflies and moths have two functional pairs of wings that are covered in scales, arranged like shingles giving them their beautiful appearance. This group has a very unique way of dealing with drag, called wing coupling. In the video below,the cabbage looper (Family Noctuidae) is shows frenate coupling, where a well-developed hair (called a frenulum) on the hind wing catches with the forewing (called retinaculum). During flight, you will notice both pairs of wing appear “together”.
Another great example of wing coupling is in bees and wasps (Order Hymenoptera). They have hooks (called hamuli) along the top margin of the hind wing that catchinto the fold of the front wing. The number of hamuli are quite variable among this order, some only have a few and the larges wasps have many. You can see both pairs of wings work together in the below slow motion video of a Polistes (Family Vespidae) take off. One unique adaptation in this family of wasp is that the hind wing is longitudinally (lengthwise) folded under the forewing at rest. In this video you can see the hindwing unfold from the forewing and spread open for flight.
Scientists study insect (and, more recently, hummingbird) flight for their potential application in advanced engineering, robotics, and aviation. The problems that insects have had to overcome, such as turbulence, stabilization, and maneuverability, are the same we continue to face as we endeavour faster and more efficient crafts. We still have a lot to learn from insects!!
McCann, S. Dragonfly in Flight. [Cover Photo] 2012. Flickr, Vancouver, BC, Canada. Web. 08 Aug. 2014. <https://www.flickr.com/photos/deadmike/7604870044/in/photolist-fctMDR-fctMJP-cA1WV3-fctMXP-8Ya1k-aeu2QA-arHaS/>.
ValeVids. “Dragonfly action in slow motion.” YouTube. YouTube, May 31, 2010. Web. August 3, 2014.