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|Aeshna juncea hovering over a pond.|
Like most of the flying insects (flies, beetles, Lepidoptera and Hymenoptera), they evolved in the early Mesozoic era. Their prototypes, the giant dragonflies of the Carboniferous, 325 mya, are no longer put in the Odonata. These are now called Protodonata or Meganisoptera.
The two suborders are easily distinguished:
- Dragonflies: they are Anisoptera (= usually larger, eyes together & wings up or out at rest)
- Damselflies: they are Zygoptera (= usually smaller, eyes apart & wings along body at rest)
All Odonata have aquatic larvae called 'nymphs', and all of them, larvae and adults, are carnivorous. The adults can land, but rarely walk. Their legs are specialised for catching prey. They are almost entirely insectivorous.
These insects characteristically have large rounded heads covered mostly by big compound eyes, legs that catch prey (other insects) in flight, two pairs of long, transparent wings that move independently, and long abdomens. They have two ocelli (eye spots) and short antennae. The mouthparts are on the underside of the head and include simple chewing mandibles in the adult.
- The Biology of Dragonflies. CUP Archive. 2018-10-13. p. 324. GGKEY:0Z7A1R071DD. https://books.google.com/books?id=J584AAAAIAAJ&pg=PA324. "No Dragonfly at present existing can compare with the immense Meganeura monyi of the Upper Carboniferous, whose expanse of wing was somewhere about twenty-seven inches.".
- Grimaldi, David; Engel, Michael S. (2005). Evolution of the Insects. Cambridge University Press. pp. 175–187. https://archive.org/details/evolutioninsects00grim.
- Hoell H.V., Doyen J.T. & Purcell A.H. (1998). Introduction to insect biology and diversity. 2nd ed, Oxford University Press. pp. 355–358. .