LEPS & ODES: Dragonfly mass emergence in progress
As you read these words, locally the biggest event of the dragonfly year is well underway: a mass emergence.
In just a few days, hundreds if not thousands of dragonflies will be suddenly on the wing.
I.D. mix up
Before venturing into the 2018 phenomenon, I'll transport us back to May 1994. During a visit by 10-year-old grandson Jimmy, we were surrounded by many rusty-brown dragons who seemed to be everywhere near our log home on Spider Lake.
A few weeks later, after Jimmy had returned to Omaha, I saw a lot of black dragons with impressive bright-white markings. Back then I thought this was a totally different species, but I was wrong. Not until a few years had gone by did I find that the two "different" species were in fact one: the Chalk-fronted Corporal. How could this be? They looked so different!
Unlike butterflies whose colors don't change during their brief lives as adults, dragonflies experience a dramatic color transformation. They are actually immature when they emerge. (Shortly I'll get to the emergence phase.) They need to age one to one-and-one-half months to become sexually mature. The rusty-brown Corporals that Jimmy and I saw were immature. The dramatic black-and-white ones with chalky-white "corporal stripes" are mature males. (Female Corporals do turn gray, but lack the white stripes and tips of abdomens that the males develop.)
Of the many amazing aspects of dragonflies, I would rate the dual lives feature as the most amazing. About 30 years ago, I became fascinated with flying dragonflies and started taking pictures of them.
I only thought of them in terms of their flying. At the time, my ignorance of their dual life cycle was understandable. Little information was available for a lay person such as me. (Happily that has changed for the better!)
I was surprised, but should not have been, that most of their lives is spent as underwater larvae. Depending on the species, that amounts to one to seven years. While underwater, they breathe dissolved oxygen. They are fierce predators, feeding on such prey as mosquito larvae.
Eventually, something triggers the move to their next state: flying adult. Prior to leaving their underwater domain, the larvae rise to the surface and start breathing air. They climb up on such things as vegetation. Then, like a parachute released in slow motion, the back of the larva splits open. The adult pushes its way out. The abdomen extends and wings unfurl. In about an hour, the "teneral" (as young adults are called) begins its aerial life. The shed skin, called "exuviae," remains behind.
As a flying adult, it will feed on flying insects, such as mosquitoes, gnats and flies. Once fully mature, it will mate, eggs will be laid and the cycle will continue as larva grow underwater.
Perils to dragonfly larvae as they emerge are high. Studies have found up to 90 percent mortality from birds.
To somewhat counteract mortality's impact, nature employs a strategy that could be termed "strength in numbers." That's what the mass emergence is all about. Though the rate can still be as high as 90 percent from adult birds and their newly-hatched babies as well as from other wildlife, the surviving numbers of dragons are considerably higher when thousands rather than a few dozen are in jeopardy at the same time.
Marlene and I have even seen a few Corporal larvae that crawled a 100 feet through our wildflower meadow to emerge on our log home itself. They avoided the highest risk zone at the shore.
I've noticed just a few species of dragons participate in this spring mass emergence: Dusky Clubtail, Spiney Baskettail and the already mentioned Chalk-fronted Corporal.
During our extended 2017-18 winter, I finally finished adding all the dragonfly sightings I had from 1997-2017. The 21-year total exceeded 163,000! Of the 58 species I've tracked, Chalk-fronted Corporals' 68,262 represent the lion's share at 42 percent of the total.
On Memorial Day this year I encountered 405 Chalk-fronted Corporals in just one-third of a mile from our home.
For today's column I did something I'd never done before. I constructed a table for the seven most recent years for what I've seen at Spider Lake. The seven-year average ice out is April 19, with May 29 as average start date for Chalk-fronted Corporals' emergence. An average of 40 days separate those two events.
Looking at that table, I find it very interesting that the two years with the latest ice outs had much shorter gaps than the 40-day average.
Normally, leading up to the mass emergence, large clouds of white "gnats" (I call them) hover as swirling galaxies two feet or more across. They are the first insects the teneral Chalk-fronted Corporals eat. I was troubled this year; no large gnat clouds ever formed. What I did see were very few and very small. Is this another case of climate change getting things out of sync (in this case, predator-prey relationship)?
However, there is a rule-of-thumb that a new mosquito generation will go from egg to flying adult in just 10 days in northern Minnesota. 2018's newly emerged dragons should still be on "active duty" when the next generation of mosquitoes go on the attack.
Things you can do to help dragonflies
• Buffer strips: Enhance water quality by being last line of defense keeping pollutants, nutrients, etc. from leaving shorelines. In particular for dragonflies, buffers provide vegetation for larvae to climb as they emerge as flying adults.
• Drive slower (if possible): Dragonflies are cold-blooded. During the cooler times of the day they rest on drives and roads until their flight muscles warm up. So, driving slower when you see them resting can allow they to safely take off when you approach in your vehicle.
Ice Out Date Date Corporals Number Days
For Spider Lake Start Emerging After Ice Out
2012 March 30 May 22 53
2013 May 11 June 7 27
2014 April 27 May 31 34
2015 April 13 May 26 43
2016 April 14 May 23 39
2017 April 8 June 4 57
2018 May 2 May 24 22
7-year Avg. April 19 May 29 40 days
John Weber is a local butterfly and dragonfly enthusiast. Since 1997, Weber has been meticulously recording every dragonfly sighting. He’s counted butterflies since 1993. “Leps” is short for the insect order of lepidoptera, meaning butterflies and moths. “Odes” is short for odonata, or dragonflies and damselflies.