Monday, July 1, 2013

The Dragonfly: Master of Flight

Slaty_Skimmer_on_flowerThe ability of a flying animal to move through the air varies greatly, with some creatures possessing an exceptional mastery of this skill. While many forms of life simply use their aerial capabilities to quickly and efficiently travel from one place to another, others have evolved extraordinary airborne talents. Bats, swallows and swifts are all well known for their highly maneuverable style of flight, allowing these hunters to pursue and capture bugs in the air. Yet, from an aerodynamic perspective, the most unique and complex flying creature in the Adirondacks is the dragonfly, which must be considered the true master of flight.

The dragonfly actually represents a group, or order, of insects known as Odonata, which encompasses many species of both dragonflies and damselflies. All of the individuals in this category have evolved a highly complex flight style produced by their two sets of long, slender and transparent wings.

Rather than function together, as is the case with nearly all flying creatures, each of the 4 wings of the dragonfly can operate independently of the others. Additionally, a dragonfly is capable of subtly altering the shape, or curvature of each wing which impacts the amount of lift that the surface generates. A dragonfly can also twist each wing, or change the pitch with respect to the plane of its body, which further impacts the amount of upward force that this structure produces. As a pilot knows, increasing the pitch of a wing increases the “angle of attack,” which results in more lift. Too high a pitch, however, can abruptly cause the flow of air over its surface to stop resulting in a “stall” or the cessation of lift. By synchronizing its four wings together, the dragonfly can achieve an exceptional amount of lift, which enables it to quickly burst into flight. Some researchers have measured the dragonfly accelerating upward at nearly “4g” which is roughly the same as the space shuttle achieved during the first few minutes after its lift-off.

The rate of wing beat, along with the amplitude of each beat, provides for the amount of thrust which determines the speed at which the dragonfly moves forward once it becomes airborne. Like a hummingbird, a dragonfly has the ability to move rapidly when the need arises.

By beating its front wings one way and its rear set in an opposite manner, the dragonfly can hover in one spot. This allows this insect the opportunity to scan the immediate surroundings with its exceptionally large and well developed eyes for aerial prey or the presence of potential predators. By beating the wings on one side of its body together, and wings on the other side so that these two cancel, and provide no forward motion, the dragonfly can pivot or spin faster than any other flying animal. Since each wing is capable of producing its own lift, thrush, drag and downward pull, the dragonfly’s aerial maneuverability is unmatched on our planet.

As aviation buffs are aware, the ability of an aircraft to perform depends on the conditions of the atmosphere. Air that is saturated with water vapor greatly reduces the capabilities of a plane, as does the presence of low pressure. The moist or humid air that has settled over the region makes it harder for all creatures to fly, and the absence of strong high pressure so far this season has compounded the challenges of flight.

In order to operate its wings, the dragonfly relies on tiny sets of muscles that require substantial warmth to function continuously. Even during mid summer, when the sky is clear and the temperature is well into the 80’s, it is quite common for a dragonfly to rest on the top of a plant with its back and wings turned toward the sun. This enables the body and muscles of this insect to absorb the thermal energy needed to permit long periods of flight. It is on sunny days in summer when dragonflies are most commonly seen patrolling a section of lake shore, a backyard, or along the side of a road. When the weather is overcast, or rainy, and the amount of solar energy is low, dragonflies tend to remain grounded.

Although negatively impacting the dragonfly, the damp and dreary conditions that have generally prevailed across the Adirondacks since the end of May have benefited the population of many bugs, like mosquitoes. As a general rule, mosquitoes strongly prefer the moist air that develops around sunset and continues through the night. While some naturalists believe that this is caused by the mosquito’s sensitivity to the dry air that develops during the daylight, others are sure that it is to avoid an encounter with an aerial predator that can not be eluded.

Photo: A male Slaty Skimmer (Libellula incesta), courtesy wikimedia user D. Gordon E. Robertson.

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Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

One Response

  1. Adkdave says:

    Hey Tom. What a great article! Dragonflies are always a welcome companion while resting on on the shores of a warm adirondack afternoon. And what a flyer! Makes me want to get out there and do some flying too.

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