Charles Darwin is along Shoal Creek at every corner, in every niche. All that I see, every bird, bush, and bug, is spilling forward to an obscure Darwinian end. Life is too brief to see how quickly the world evolves around me. I am not here long enough to witness the changes for myself. Instead I imagine.
I understand the principles, so I apply them to what I see. I conjure images of a fast-forward evolution. Image and imagine are both from the Old French imaginer. Image originally meant “to form a mental picture,” precisely what I do in my Darwinian moments.
Dragonflies are Darwin on steroids. A dragonfly may live a year or more, but most of that time is spent as a nymph plowing through the muck at the bottom of a pond or stream. Dragonfly nymphs are the stuff of legend; there are few more voracious predators. With an extendable lower jaw, the nymphs nail fish and other prey the way that the acid-salivating monster in Alien made quick work of the crew. Dragonflies live most of their lives as nymphs.
The ugly duckling transforms into a swan in summer. The nymphs fix themselves to stems and branches near the water, metamorphose, and emerge from their shells (exuvia) days later as dragonfly tenerals. The tenerals then perch for a few hours while hardening and extending their wings. With a few flaps the adult dragonflies sweep off to capitalize on the few weeks they will enjoy as adults.
Dragonfly life is simple and brief. Eat. Mate. Die. Without this simplicity, Darwin’s evolution fails.
First, dragonflies eat. As nymphs they crave meat. Nymphs consume mosquito larvae like we gobble potato chips. They also relish other aquatic insects and worms, and small aquatic vertebrates like tadpoles and small fish. Adult dragonflies eat just about anything that is edible and can be caught. Unlike purple martins (sorry, they eat larger insects), dragonflies keep mosquito populations under strict control by feasting on them when they are in abundance. They also feed on ants, termites, butterflies, gnats, bees, and other insects (including other dragonflies). Look at it this way. If dragonflies were as large as vultures, we would all carry shotguns.
Dragonflies mate. Survival in itself is an evolutionary dead end. Dragonflies must reproduce.
A brief life as an adult precludes any court and spark. Dragonflies cut to the chase. Males grab females as they float by and wrestle into position to deposit their sperm. Some male dragonflies leave a plug in the female after mating to keep other males from stealing their thunder. In the dead of summer (high time for dragonflies) there is no pond, puddle, creek, or river that is not swarming with breeding dragonflies. Female wandering gliders often try to lay eggs in the sun reflecting off of the hood of my car. Gravid females dip their tails into the water to deposit eggs (ovoposit), and males hover over the laying females to ensure that their sperm isn’t replaced by another male sneaking in on the action at the last minute. No love is lost where there is no love.
Only a few eggs will survive to become nymphs. Nymphs prey on fish; fish prey on eggs. While photographing a darner (another type of dragonfly) over a small pond near Las Cruces I watched in horror as a largemouth bass burst out of the water and gobbled it whole. Mississippi kites are especially fond of dragonflies, dismantling them, piece by piece, on the wing. When the survival rates are low, adults must produce copious numbers of young. There is no nurture, only nature, with dragonflies.
Evolution demands countless generations to combine minuscule advantageous changes to form a new organism. These countless generations need adults to die and get out of the way. Once the young have been raised, adults are castaways. Dragonflies are generous in this regard; adults rarely live longer than a couple of months.
But what a show while it lasts! The best time to see dragonflies in Austin is during the hottest time of day during the hottest season. Dragonflies are an earned experience. Poke around Shoal Creek or Pease Park any afternoon during the next month or so and you will see them by the hundreds. Take even more time and walk around Lady Bird Lake and you will see thousands.
Dragonflies tolerate poor water quality better than damselflies, but both depend on the quality and consistency of a flow in Shoal Creek. Do you want a simple way to control the mosquitoes in the yard? Let’s get more consistent flows into Shoal Creek and allow the odonates (both dragonflies and damselflies) to proliferate.
Enjoy this time of year along our creek. Keep an eye out for the old man. He appears in the oddest places, but his presence is always felt.
Ted Lee Eubanks
30 July 2013