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The Carletonian

The Carletonian

The Carletonian

Jurassic Arb: Odonata in the Cowling Arboretum

<agonflies and damselflies compose the order Odonata, a clade of winged, carnivorous insects whose modern families emerged and diversified during the Jurassic and Cretaceous periods between 200 and 145 million years ago. Prior to this, other species of dragonflies ruled these prehistoric skies. Meganeuropsis permiana was the largest flying insect ever to evolve on Earth, its wingspan reaching nearly 70 cm (27 in) in length. Fortunately for us, these dragonflies met their end in the Permian Mass Extinction. Fossils of this species are known only from the American Great Plains region, not so very far away from where our Arb now stands.

Today, the Odonata on Earth are much smaller, the largest only 19 cm (7.5 in). Indeed, they will never achieve such gigantism again. All insects utilize a series of tiny tubes to breathe via diffusion, rather than lungs, and larger insects require more oxygen. During the Permian Period, the Earth’s atmosphere contained 10-15% more oxygen than modern levels, and thus, conditions were able to sustain larger insects.
So where can I find a dragonfly, you may be asking? There are, in fact, about 50 species of Odonata found in the Arboretum, 35 of which are presently in flight season. Whereas damselflies remain fairly close to their parent stream or pond during their adult lives, dragonflies wander further afield. Look for species such as the Common Green Darner (Anax junius)—the Arb’s largest and most long-lived species—and the Wandering Glider (Pantala favescens)—the dragonfly that flies across an ocean—above our prairies; the Twelve-Spotted Skimmer (Libellula pulchella)—one of the Arb’s more striking species (pictured below)—around Kettlehole Marsh; or even walk across the fields behind the Rec, which boast many a White-faced Meadowhawk (Sympetrum obtrusum).

Why are dragonflies considered to be among the most dangerous predators on the planet? How long to they live? Where do they go in the winter? To have these and all your Odonata-related questions answered, join the Student Naturalists on a Dragonfly Walk in the Arb on Saturday, September 22 (second week), leaving from the Arb Kiosk at noon. See you out there!

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