Female green darner left, laying eggs. After mating, the male will remain attached, guarding against other males’ mating attempts; a successful challenger will scoop out this male’s sperm and deposit his own.
Photo: NPS-Ken Slade
Dragonflies: Our Tiny, Hungry Year-Round Neighbors
By Kevin McKeon, Maine Master Naturalist
Dragonflies first appeared on Earth before the dinosaurs, about 300 million years ago, growing to almost 3 feet long. It’s believed that the higher oxygen levels (35% then, 21% today) combined with the lack of other flying creatures to prey upon them allowed these so called griffinflies to become some of the largest insects to ever exist. Today, the largest dragonfly is the 6.3-inch giant petaltail, which lives in Queensland, Australia; in the U.S., it’s the giant green darner; and in Maine it’s the common green darner.
The differences between dragonflies and darners are subtle to us trail walkers; there are also damselflies, which are smaller and dainty-looking, and tend to hold their folded wings over their back — a critter for a future story. But if it’s big, with eyes that are very close together or even connect, it’s probably a darner — though it might be hard to get close enough to tell! Taxonomically, they both fall under the order Odonata, and darners under the lower family Aeshnidae. So, a darner is a dragonfly, but not all dragonflies are darners. Since our green darner is quite common along our Sanford trails and meadows, and the most common in the U.S., knowing a bit about them may be enjoyable.
Pair of mated autumn meadowhawk dragonflies laying eggs in a backyard water garden.
Photo: Kevin McKeon
So yes, these green darners, Anax junius — “Lords of June” — are big at 3 inches long with a 4-inch wingspan and yellowish-veined wings. Both sexes have green mid-sections (thorax). Females’ tails (abdomen) are generally brownish-orange, but can vary; males are black and bright blue. After mating, single eggs are deposited into slits the female makes in wetland plants — the only North American darner to use this method. Aquatic nymphs emerge a few days to a few weeks later, depending upon the climate zone within their migratory route. The nymphs, like their parents, are ferocious predators that eat almost any other water-dwelling animal they can catch. After one to three years, and up to 12 molts — again, depending upon the climate zone — it’ll crawl up the water bank or climb up a plant stalk where the final molt happens. This is a form of metamorphosis, resulting in the emergence, called eclosion, of our adult dragonfly — the bane of all airborne insects!
Our green darner, like all dragonflies, can’t hear, smell, vocalize, or even with its six legs, walk! Its brain power is concentrated on predation, and it’s about the best on Earth, with a 97% success rate. With a sense of sight that allows ultraviolet and polarized light vision at almost 360º around itself, 37 mph flight speed, and an appetite requiring about one-third its body weight of food per day, the darner gives any insect within sight poor prospects of living very long!
Green darner migrations, exhaustively studied and published in Biology Letters, are comparable to our monarch butterflies. Spanning at least three generations of green darner life, its annual life cycle begins with emerging from its aquatic nymphal home in the southern U.S./Mexico areas to begin its migratory flight of up to 1,550 miles. Our Sanford dragonfly may have begun near Florida or near Mexico, flying about 80 miles a day. It’ll be among the first insects to appear in May, when it’ll mate, lay eggs, and die. After emerging from these spring-laid eggs, some of these nymphs will remain in their wetland home for years; others will grow quickly, metamorphose to second-generation adults, and begin to head south in late summer/early fall — when they’ll mate, lay eggs, and die. These third-generation eggs then eventually mature into adults, which are non-migratory and over-winter in their warm climate where they’ll mate, lay eggs, and the resultant offspring migrate north to renew the cycle.
Green darner emerging from its final nymph stage. It will remain, clinging to its shell, for about an hour until it swells with fluid and dries.
Photo: Patty McKeon
The indigenous Navajo held dragonflies to be a symbol of water purity, and modern science agrees. Because some dragonfly nymphs live for up to five years, the National Park Service’s Dragonfly Mercury Project works with citizen scientists and community volunteers to collect dragonfly larvae for mercury analysis. This project produces the largest data base for mercury contamination and environmental risk in the U.S. Get involved here.
Migration Study: https://pmc.ncbi.nlm.nih.gov/articles/PMC6303508/
Monarch butterfly migration: https://sanfordspringvalenews.com/out-in-the-woods-85/
NPS Dragonfly mercury study: https://www.nps.gov/articles/dmp-get-involved.htm
Editor’s note: Did you see something unusual last time you were out in the woods? Were you puzzled or surprised by something you saw? Ask our “Out in the Woods” columnist Kevin McKeon. He’ll be happy to investigate and try to answer your questions. Email him directly at: kpm@metrocast.net
The post Out in the Woods appeared first on Sanford Springvale News.
