In August, 2010, my family and I watched from our backyard an unbelievable phenomenon: a single species of dragonfly, individually numbering in the thousands, flew steadily westward across our property on the edge of town for ten magical days. Occasionally they would perch briefly – each one facing west – on the neighbor’s wire fence before continuing on.My mind went wild with questions: Were they migrating? What species were they? Where had they come from and where were they all going? I hiked up the hills due west of us along their line of travel, to see if they were indeed continuing on, instead of, perhaps, stopping at the local creek. Turns out the same species was flying west up and over the hills and out of sight.
A digital camera and the internet turned out to be a big help that first year. A wonderful woman in Arizona helped me identify the species, Sympetrum corruptum, commonly known as the variegated meadowhawk. After writing to the author of a guide book on dragonflies, I found out that this species is migratory along the Pacific coast, but reports of them migrating within or through Montana are apparently unknown.
According to the Xerces Society for Invertebrate Conservation, 16 North American dragonfly species make migrations, including our own variegated meadowhawk. Apparently large body size is a prerequisite of insect migration, since only those species with large flight muscles can attain the flight speeds needed to overcome ambient winds. So it’s no surprise that within the insect world, only some dragonflies, butterflies and moths are known to migrate.
While certain moths migrate by passively using air currents, migratory dragonflies, in the same way as the well-known monarch butterfly, undertake directional movements regardless of prevailing wind direction. This is certainly what we witnessed during our meadowhawk event two years ago. Every individual dragonfly we observed over more than a week’s time was headed west despite headwinds that seemed to ground some of them in the tall grass for short periods of time.
A Xerces report comments that scientists currently studying migratory behavior in dragonflies are in about the same position as researchers studying monarch butterflies 40 years ago: we know a phenomenon exists, but most of the details remain to be worked out. This is one thing that made our meadowhawk spectacle so exciting. Citizen scientists have much to contribute to our collective understanding of dragonfly migration, if that is indeed what we were witnessing.
Xerces co-chairs a unique collaborative, the Migratory Dragonfly Partnership, or MDP. According to the MDP website, one of their missions is to develop an international network of citizen scientists to monitor the spring and fall movements of the main migratory species in North America.
The primary volunteer project within the MDP is the Dragonfly Pond Watch: if you live near a wetland, or visit one regularly, you can offer up your observations of the annual movements of two specific migratory dragonflies, one of which can be found in Montana: the common green darner. Our scientific understanding of dragonfly migration can be advanced by widespread observational data, which thoughtful, interested citizens across the country are perfectly poised to gather.
In August 2011, at Smith Pass in the Swan Range, I watched what may have been another migratory event, hundreds of dragonflies moving west over the snow-covered divide at about 7,900 feet! While I wasn’t able to catch any of these for proper identification since they flew so far overhead, the event further spurred my interest and made me hope that we can develop a network of interested citizen scientists who can make and compare their observations of these fascinating insects.
"Field Notes" is produced by the Montana Natural History Center.
(Broadcast: "Field Notes," 7/07/15. Listen weekly on the radio, Sundays at 12:55 p.m., Tuesdays at 4:54 p.m. or Fridays at 4:54 p.m., or via podcast.)
