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-------------------------- 2429 - DRAGONFLIES - we have a lot more to learn ?
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- My grandson Michael loves to watch the dragonflies over my pond. They were mating and laying eggs in the water. The larvae come to the surface and the dragonfly sheds its shell and fly’s off.
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- Some new things are just being learned about dragonflies as we use some of the latest technologies. Scientists have attached ultra light transmitters to the underside of common green darners (anax junius). Green darners are robust fliers with blue abdomens that turn purple as the temperature rises. The transmitters cost $200. They attached the transmitter to abdomens using eyelash adhesive. (Can’t you just see Michael doing this).
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- The transmitters are one-third the weight of the dragonfly, but the dragonfly could handle the extra weight with ease. They did this to 14 dragonflies. They used chase vehicles and a small plane to follow the flies. The dragonflies covered 37 miles in 6 days. The flies behaved like a flock of birds. They stayed put when the winds got above 15 miles per hour.
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- Studies like these have discovered that at least 9 of the North American dragonflies are migratory. There are 5,200 species of dragonflies and damselflies in the world. Scientist now estimate that at least 50 make seasonal migrations.
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- In Wisconsin the emerald dragonfly (Somatochlora hineana) are considered endangered. The insect takes 4 to 5 years to mature from an egg into a green-eyed emerald dragonfly. It spends the years in the water as a six legged larvae voraciously eating other little aquatic creatures. At the end of their larval form they pull themselves out of the water onto a perch and shed their skin. And, off they fly.
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- Scientists can find the cast-off skins and the barely distinguishable dot on an exuvium’s underside indicates that it came from a male. (The larvae themselves are near impossible to find and count). The study found that the sexes reached adulthood in equal numbers. However, in the wet land breeding grounds there were twice as many males as females.
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- If they were to help to save this endangered species they had to learn what happened to the females. Further exploring found the females were found in the dry meadows, not the best feeding areas. So, what was causing this behavior?
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- More observations and the conclusion was sexual harassment had driven females to avoid the male-dominated turf. Males of several dragonfly species are known to sabotage each other’s mating attempts by scraping the previously deposited sperm out of the a female’s reproductive tract before delivering their own.
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- Many males guard their mates, even dragging a female around by the neck after mating. Some males are so relentless to mate they force a female to the ground and even with the female cooperating can spend more than an hour in an encounter. So, no wonder the females stay away from the guy zone unless specifically seeking a mate and laying eggs.
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- Another strange behavior occurs in the larvae stage. Red devil crayfish (Cambarus diogenes) share the wetlands where emerald dragonflies live and dines on the emerald larvae. The crayfish live in stream-bank borrows and the larvae were found in the same borrows.
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- A quick decision could have been let‘s cull the crayfish and we will have more larvae to save this endangered species. Wrong again. The crayfish structures provide a life-saving refuge for the dragonfly larvae during the summer droughts. Even if some get eaten it is a good trade off for the species to have a wet hole to live in during the droughts.
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- Female dragonflies shy away from fish-filled waters when choosing sites to lay eggs. Somehow they know that fish readily eat dragonfly larvae. Dragonflies eat bees and some how bees are found pollinating St. John’s worts and broadleaf arrowhead plants near the edges of ponds that have fish because most of the dragonflies are around the ponds that have no fish.
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- How do these little brains figure all this stuff out?
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- Wetlands are disappearing fast and biologists are concerned that more than 100 species of dragonflies and damselflies are endangered.
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- If dragonflies become rare they are one of few insects that people might miss. Judging by dragonfly earrings, fabric patterns, Christmas lights, garden art,….. people like dragonflies.
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- There is a lot more that we need to learn more about dragonflies.
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- August 3, 2019 676
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--------------------- Saturday, August 3, 2019 --------------------
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