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Featured Species: Dragons and Damsels!
Late-June is a great time to visit water bodies, in part due to the activities of dragonflies and damselflies, the needle-like insects patrolling the water. A captivating 30 minutes can be spent watching an adult emerge, and if your timing is right you may be lucky enough to be amidst a swarm mating or otherwise.
Dragonflies and damselflies have large, ancient ancestors that existed at least 300 million years ago (they rubbed elbows with dinosaurs and the creatures that came before). Dragonflies and damselflies can be told apart by their general shape, and the way the wings are held at rest. Dragonflies are larger and hold their wings open, whereas damselflies are daintier looking and hold their wings together or slightly spread. As larvae (called nymphs) dragonflies are larger, while damselflies are slender and have leaf-life gill appendages at the end of their abdomen. Six common dragonfly families include (Darners, Clubtails, Spiketails, Cruisers, Emeralds, and Skimmers), and three damselfly families you may encounter are (Broad-winged Damsels, Spreadwings, and Pond Damsels). Dragonflies and damselflies easily capture the imagination, and names like ‘boghaunter’, ‘dragonhunter’, ‘jewelwings’, ‘shadowdragon’, and ‘sprites’ help. Dragonflies and damselflies become common sights in late spring and remain so all summer. Different species emerge at different times. Here are some species emerging in late June:
Dragonflies and damselflies are of two worlds - nymphs are freshwater aquatic (and quite predaceous!), and the adults are terrestrial (and thankfully eat lots of mosquitoes!). Their lifecycles are described as an incomplete metamorphosis since there are shape changes but they do not undergo an inactive pupae stage. At this time of year mature nymphs make their way to water’s edge and onto vegetation, rocks, and logs. Then out of the back of the larvae’s skin emerges the adult (this is better than science fiction!). Next, over about 30 vulnerable minutes, the adult’s wings unfold as their insect blood (haemolymph) flows into the fine veins. Then they fly to protective cover to harden and sexually mature. The nymph skin (exuviae) remains clasped to the vegetation, rock or log, as evidence of what occurred and where. Once hardened and matured, adults disperse to feed and mate. Sometimes thousands of a single species will emerge on the same day, which is thought to maximize the chance of finding a mate.
Mating is another mind-bender. First the male transfers sperm from his sexual organs at the end of his abdomen to other sexual organs located closer to the wings. Then using claspers at the tip of his abdomen, the male locks onto the female behind her neck – this is the ‘tandem position’. Should the female like the guy, she brings her sexual organs up to where the sperm is – this is the ‘wheel position’. In some species the male is adapted to remove (1:00) any sperm already within the female before depositing his own. The pair separate, and the female lays her eggs. In some species, the male continues to hold on or stays close to make sure another male doesn’t mate with her. Most eggs are laid in water, but some species inject eggs into aquatic plants. When eggs hatch the nymphs feed and over-winter underwater.
Common Green Darners exhibit both this typical life style of over-wintering as aquatic nymphs, and also as migratory adults that spend our winter in the southern states. Radio-tagging research has showed that they may fly up to 140 km in a day. Migratory individuals arrive north as early as the beginning of April and mate and lay eggs right away. The nymphs develop quickly (for dragonflies) over the summer, and adults emerge ready to migrate in late August through October.
It is the end of another school year. We have enjoyed bringing you some of the fascinating events that have happened in the natural world over the past 10 months, and look forward to starting again in September. Have a great summer!