Blue Dasher Dragonfly

August 13, 2011

Dragonflies_10Jul2011 (2)


Photographers: John W. Ehman; John's Web site and Jean LeBlanc; Jean's Web site
Summary Authors: Jean LeBlanc; John W. Ehman

These two Blue Dasher dragonflies (top photo) demonstrate the amazing aerodynamic abilities of this insect. The intricate wing structure (top and bottom photos) is apparent in the still wings of the one, while the functional capacity is illustrated in the hovering of the other in this face-off between two males at a lily pond. Dragonflies (Pachydiplax longipennis) have two pairs of independent wings that can beat either in or out of phase, modulating the amount of lift and drag. When hovering, the wings stroke back and down in a kind of rowing motion that creates vortices of air and upward drag: complex fluid dynamics instrumental in keeping the body stationary. The efficiency of the wings is increased by their capacity to flex and twist with the air. This natural action conserves energy that the insect would otherwise have to use to effect such turns by exercising muscles. The wings in the foreground also show a solidly colored (dark) cell called a pterostigma, which by its slightly heavier construction helps dampen vibrations and assists in gliding. Dragonflies can fly over 30 mph (48 km/h) and can even fly backwards. Research into their aerodynamics has been used to further the design of specialized aircraft and even wind turbines.

Dragonflies consume huge quantities of smaller flying insects, earning the nickname "mosquito hawks." Three-hundred-million-year-old fossil dragonflies are evidence of a very different atmosphere than we experience today, one so oxygen-rich that these insects' wingspans could reach two ft (0.65 m). They may have been one of the first insects and one of the first animals of any kind to evolve flight. Nearly 30,000 lenses make up the compound eye, giving the adult dragonfly a 360-degree field of vision (bottom photo). Find a favorite spot by a pond or stream and observe these wondrous creatures for yourself.

Top photo taken July 10, 2011 from Upper Darby, Pennsylvania. Bottom photo of a male blue dasher was taken on June 29, 2011, at Kittatinny Valley State Park in Andover, New Jersey

Photo details - Top: Leica DG Macro-Elmarit camera; 45mm lens on a Lumix G1 body; Focal Length: 45.0mm (35mm equivalent: 90mm); Aperture: f/11.0; Exposure Time: 0.0020 s (1/500); ISO equiv: 200; Exposure Bias: none; Metering Mode: Spot; Exposure: aperture priority (semi-auto); White Balance: Auto; Light Source: Unknown; Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.

Bottom: Camera Maker: Canon; Camera Model: Canon PowerShot SD750; Focal Length: 5.8mm; Digital Zoom: 3.000x; Aperture: f/2.8; Exposure Time: 0.0020 s (1/500); ISO equiv: 80; Exposure Bias: none; Metering Mode: Center Weight; White Balance: Auto;Flash Fired: No (enforced); Orientation: Normal; Color Space: sRGB.