This is regarding dragons and damsels. Flies that is. On my property in Oregon, USA there are many different species. I was observing a group of Blue Eyed Darners(Rhionaescha multicolor according to my guidebook). There is a kind of stroboscopic effect as their wing flapping has a very short stroke and the center of this stroke happens twice per cycle. When they are flying directly towards you, they seem to have a biplane appearance as the rear wings are mounted lower on the thorax. Incredible fliers. Sixty kilometers per hour in a straight line. Change of direction or altitude in a flash. I often wonder if they can independently control the speed, dihedral, and angle of incidence of each wing. I closely looked at the wing of a dead specimen. The venation, of the leading edge and "spars", is composed of a series of rectangles for maximum rigidity. The trailing edge is a series of pentagons composed of two ninety degree angles at the trailing edge and the inner portion made from three sixty degree angles. The center part of the wing is made up from a series of random "lozenge like" polygons to maximize flex and create a pocket of air on the downstroke.
Many of the males and females of the same species have different colors and markings. Today, I spotted a female River Jewelwing damselfly, male Varigated Meadowhawk,male Flame Skimmer,male Widow Skimmer, plus male and female Blue Eyed Darners which are the most plentiful.