It’s the dead of winter and, hot cup of tea nestled in my hands, my feet propped up in front of the woodstove and clad only in my long underwear and wool socks, my mind (as it often does) drifts to the topic of dragonflies. I try not worry about my summertime friends, but questions do arise…
If dragonflies are primarily tropical insects (which scientists consider them to be), what are they doing inhabiting the frigid Upper Midwest, let alone well above the Arctic Circle? The answer to that question has not been fully explored but some ideas have come out of the limited research in cold weather climates, mostly done in northern Europe.
So, we know that the adults do not hibernate here, and they spend their entire sub-adult life underwater. I do some ice fishing where I live in NE Minnesota and, because I do not own a gas-powered ice auger, my arms happen to know the full implications of ice which will occasionally reach four feet or more in depth. Some of my favorite dragonfly haunts are shallow lakes with a maximum depth of 2-3 feet and most of my favorite bog habitats may have no open water at all. What happens to dragonfly larvae in the winter when they cannot escape to open water? When we speak of the wintering strategies of dragonfly larvae there are some general answers to this question. Species by species, though, it’s much harder to speak with any authority as very little work has been done on North American, cold-climate dragonfly species.
Here are the generalities:
Because we do know that many dragonfly and damselfly species take more than one year to mature to adulthood, we also know that they are over-wintering, here. There are many species which take two years to mature and a few, this far north, which go four years and possibly as many as seven years to develop into adults (the Dragonhunter, for one). These multi-year species over-winter in many different larval stages. All but the earliest larval stages seem to be fairly freeze-tolerant. Scientists have actually frozen dragonfly larvae in blocks of ice, only to have them survive thawing, but the colder the ice, the lower the survival rate.
The dragonfly species which take only one year to develop into adulthood may employ another strategy for surviving the winter. Eggs laid in the spring and early summer tend to develop, hatch and grow into larvae which are mature enough to survive the winter. Because the earliest larval stages cannot survive extremely cold temperatures, eggs laid in mid to late summer often only partially develop, waiting to hatch until the spring and are called diapause eggs. The eggs simply stop developing until the winter season has passed. During the reproductive season, the likelihood that an egg will be a diapause egg increases as the season progresses and several factors may be the cause: decreasing air or water temperatures, decreasing photoperiod or the increasing age of the mother. There is likely a combination of these factors at work.
Migration is one tactic used by the Common Green Darner to survive the cold of the north. As soon as the ill winds of fall start to blow and the temperature starts to drop, the adult Green Darners amass in huge swarms and head south. The Gulf Coast states are a common destination for these insect snowbirds from the Midwest. There they lay their eggs and die. The eggs develop in an unusually short time (about 3 months), mature into adults and then fly north when things start heating up down there. The earliest record that I have for migrating Green Darners arriving in NE Minnesota is April 16th which was, unfortunately, followed by a three-day blizzard and 18 inches of snow. Luckily it was only the early birds who froze and other Green Darners came later. I have witnessed early Green Darner pairs, apparently, successfully ovipositing in the thawing rim of an otherwise frozen lake. The resulting larvae of our spring migrants develop into adults in time for the fall migration back south. To confuse our Green Darner migration situation, it has been recently discovered that, throughout their range, there is a separate population of Green Darners that over-winter as larvae. These issues are currently being researched in North America, so stay tuned…
Several years back, we had an extremely cold and dry winter, here in the north. Frost levels reached down nine feet and I know a woman up here whose well line didn’t thaw until June 12th. That year I did worry about the dragonflies. How could they survive such intense conditions? Spring finally came and I was greeted by, among all the other dragonflies, the usual swarms of Baskettails, eager to rid the warming air of our plague of blackflies, just like normal and right on time. Not to worry. They can take it!
The watchers of birds, butterflies and dragonflies revel in the colorful splendor and fanciful flight of their favorite critters. Dragonflies, with their gossamer, glittering wings soar and zoom, delighting all. Let’s take a little look behind the scenes at some dragonfly behavior, mainly, their feeding habits. Be warned, it’s a constant blood-bath.
Dragonflies and damselflies are known collectively as the Odonata. Odonata roughly translates from Latin to “the toothed ones” as is observed when a dragonfly is eating. Its jaws move side-to-side as the “meat hooks” rip and tear the flesh of its prey. The earliest record of an insect recognizable as a dragonfly dates to fossils dated back to about 300 million years. Some of these prehistoric, pre-dinosauric creatures had wingspans of about 29 inches and would probably be able to dine upon the average poodle, today.
Dragonflies and damselflies are all eyes, at least as far as their sensory input from the outside world goes. They cannot smell, they cannot hear and apparently have no sense of taste. There are as many as 15,000 lenses on each eye, and contrary to Hollywood’s interpretation of insect vision, they do not see images broken up into kaleidoscope patterns. We humans have two lenses but our brain combines the images from the lenses into one pattern and the same is true for insects, only more so. With a little swivel of the dragonfly’s head, it can see almost 360 degrees around. They are very good at seeing plane-polarized light; that is, reflected light. Light reflects off of the wings of their flying prey, making them easier to see. Try viewing dragonflies with polarized sunglasses and you will notice how difficult it is to see bugs without the benefit of plane-polarized light.
The Odonata will eat any bug that flies and, occasionally, especially true with the damselflies, will prey even on perched or walking insects. These predators will use their legs like a basket or a net to capture larger prey in flight, and will simply nab smaller prey, directly, with their mouths. The larger the dragonfly, the larger the prey that they can handle. The best example of this is the beefy, Dragonhunter (Hagenius brevistylus). They specialize in the hunting of dragonflies and the larger butterflies such as Monarchs and Swallowtails and are apparently unaffected by the venom of the bees and wasps. There are even reports of Dragonhunters taking down hummingbirds (but there is some question as to whether the dragonfly is preying upon or trying to mate with the hummingbirds).
The water-dwelling dragonfly larvae, as well, are awesome predators. Some species are stalkers, slowly hunting through the debris of the bottom of the aquatic environment in which they are maturing. Others wait to ambush invertebrates as they swim past. They may burrow into the substrate or they may be camouflaged to blend in to the background. They possess a hinged and toothed lower lip, called a labium, which shoots out to grab prey. The labium fires forward and returns at a lightning fast pace of about 1/100th of a second. The chewing mouth parts then take over ripping their food into bite-sized pieces while the labium holds it in place.
Larval prey choices range from protozoan-sized swimmers, to other Odonata larva, to mosquito larva on up to tadpoles and small fish. I know that they eat fish as my eldest daughter’s three goldfish fell prey, in one night, to a large Darner larva during my well-intentioned attempt to rear the larva to adulthood in our home.
Some municipalities in New England are looking to the voracious dragonfly as a tool for use in mosquito control programs. By importing dragonfly larvae, the hope is that the larval mosquitoes will be eaten and that the dragonflies will emerge as adults to provide some check on the adult mosquitoes. While it is true that the Odonates eat there share of mosquitoes and other biting insects, this well-intentioned attempt at chemical-free control of potential disease vectors is bound to fail, in my opinion. The following questions beg to be answered: From where are they going to get the dragonfly larvae and what affect will that removal have on the depleted area? Is it possible to collect enough larvae to make a difference? What happens to the native, endemic dragonfly populations in the targeted area? It just won’t work.
That said, enjoy and appreciate the individual dragonflies that will be attracted to the swarm of blood-sucking insects about your head in the summer.
I’m a bit obsessed by dragonflies and it all happened by accident. While working as a naturalist, in two different corners of Minnesota, I sought after and absorbed great amounts of information on such disparate topics as fossils, birds, weather, amphibians, watersheds, agates, environmental sustainability and lake clarity, to name but a few. I, like most naturalists, had become a competent generalist. That was good and that was fun but I had yearnings for deeper knowledge. I dabbled in small mammals, hoping to find or create tools which would allow the average person to identify, not only the critters themselves, but even their remains, like that which might be found in an owl pellet. I fondly remember the first time I saw a water shrew. These are truly amazing creatures worthy of study. The poor fellow had drowned in a minnow trap which I had set, as I am also very interested in the little fish.
While teaching a canoeing class at Wolf Ridge Environmental Learning Center in NE Minnesota I had a life-changing moment. Sitting peacefully on the canoe dock at Wolf Lake was a mother and her daughter and about a dozen emerging dragonflies. They had walked the shoreline, collected mature larvae that were beginning their transformation and had deposited them on the wooden platform to watch them complete their metamorphosis. Come to find out, this woman, Janet Rith, was responsible for the formation of the Minnesota Dragonfly Survey Project, a citizen-monitoring project geared to empowering citizens to collect and ID dragonflies in order to increase our understanding which species are living in Minnesota, a sorely under-surveyed region of the world.
Here was my new passion, complete with a mentor. There was very little accessible info back then so I set out to learn the complicated terminology involved in using those large, knuckle-busting books used by PhDs and graduate students. Since then there has been an explosion of regional dragonfly and damselfly field guides throughout North America. Instead of the over 350 species of dragonflies found in all of North America, the amateur can use an approachable guide containing only the species known from their area. Very convenient. Also convenient for the beginner is that most of these regional guides have translated the necessary, but potentially burdensome, scientific language of Entomology into English.
The simple act of entering the world of Odonatology (the study of dragonflies and damselflies) has enriched my life in so many ways. I have been introduced to a very gracious, warm and interesting group of individuals who love beginners and will do what they can to make their passions accessible. I have traveled, under the guise of looking for dragonflies and attending dragonfly meetings, to some very interesting parts of the world including Sweden, Louisiana and Iowa (yes, Iowa). I also now have an excuse to really get out and about in my own neighborhood to get intimately familiar with the aquatic habitats available in North Eastern Minnesota. (The intimate has come into play many times including falling into a stream with my camera, being threatened by a beaver, giving lots of blood to black flies and leeches and…well, I’ll keep you posted.)
The Upper Midwest is blessed with an abundance of dragonflies and damselflies. This area is also segmented up into several very distinct different biomes or land types which lend to a diversity of all types of critters as the different ecological niches support a variety of life. Here in the middle of the continent are conditions which cause east to meet west and north to meet south. It’s a wild region where just about anything could show up. It’s a great place to watch and identify dragonflies. Unfortunately (or fortunately, depending upon your perspective), this region is vastly under surveyed. We do not have a very good grasp on which species live where and which species are truly rare. It is often said that Minnesota, specifically, is one area which is in need of a lot of Odonate study and I have found this to be very true. New county records are not difficult to come by and new state records occur surprisingly often. Here’s an example of a new state record (in need of verification!)…
My friend, June Tveekrem, visits my area just about every summer from her home in Maryland. She is very thorough about photographically recording her finds and she and I were doing just that, last summer, in a remote area west of Finland, MN, where I live. We were in a thick swarm of the not-so-common Kennedy’s Emerald (Somatochlora kennedyi). I was catching and she was photographing. When all was said and done, we had unwittingly run across an oddball. It took quite a few emails bouncing between about a dozen Canadian and American Odonatologists to finally settle upon a pretty convincing argument that we had recorded a Quebec Emerald (Somatochlora brevicincta), known only from Eastern Canada, a few spots in Maine and from British Columbia. This was not expected, but latitude and habitat of NE Minnesota match up with the other populations. Who knew? (Which is exactly point which I am trying to make.)
The old Minnesota Dragonfly Survey Project has been defunct for several years. That’s the bad news. The good news is that the new, Minnesota Odonata Survey Project will be underway by this summer. We are seeking financial support from an interested Minnesota DNR and we have a core group of volunteers and staff associated with the Three Rivers Park District in the Twin Cities. The kick-off event for the new survey will be held during the weekend of July 7-9, 2006 at the Baker Near-Wilderness Settlement just west of the Twin Cities. There is more information about this event at http://www.cpinternet.com/~mndfly/.
We live in an Odonatologically rich part of the world and there is lot to yet be learned, here. Get involved in your region’s dragonfly and damselfly survey, if you have one, or just get out there and enjoy our many Odonata species.
Support for this project was received from the USFWS State Wildlife Grants Program, the Minnesota Game and Fish Heritage Enhancement Fund, and the Minnesota Nongame Wildlife Fund through the Minnesota Department of Natural Resources, Division of Ecological Resources.