True dragonflies showed up in the Early Jurassic skies
About three thousand living dragonfly species make up the infraorder Anisoptera, most of them tropical, and the loss of wetlands threatens them worldwide. Each compound eye packs nearly 24,000 facets. Their distant Carboniferous relatives, the griffenflies, had wingspans reaching about seventy-five centimetres.
Nymphs—naiads—hunt underwater for years in some species; adults may live about five weeks, occasionally up to ten. Anisoptera means unequal wing: hindwings broader than forewings. Crown-group dragons appear in the Middle Jurassic after Toarcian beginnings; they keep palaeopteran traits such as inability to fold wings flat against the body like neopterans. Damselflies, the other odonate infraorder, are lighter and flutter weakly, whereas dragonflies are strong, precise fliers that use motion camouflage to close on prey or rivals, and some cross oceans on migration.
Culture paints them on pottery and Art Nouveau jewelry; Japan and China use them in traditional medicine, Indonesia as food. Japanese symbolism leans toward courage and joy; some European folklore casts them as sinister. Tennyson's poetry and the prose of H. E. Bates celebrate their colour and flight.
Mating is elaborate, involving indirect insemination, delayed fertilisation and competition between sperm. The male clasps the female behind the head and she curls her abdomen forward to collect sperm from his secondary genitalia, forming the so-called wheel or heart. Much of their dazzle comes from structural colour, iridescent or metallic rather than pigment. In 2010 about 3,012 species were known, sorted into 348 genera and 11 families, found on every continent except Antarctica. One of the largest insects ever, the Early Permian griffenfly Meganeuropsis permiana, spanned around 750 millimetres. Another ancestral group, the Protanisoptera, which lacked some wing veins of modern odonates, also lived in the Permian.
Source: Dragonfly
