In 2016, JCWC volunteers began surveying dragonflies and damselflies in our watershed. Below you’ll find background on these fascinating creatures, our survey methods, and data summaries. If you’d like all the scientific details, check out the full report here!
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Dragonflies and Damselflies
Did you know…
Did you know that dragonflies are predatory, capturing other insects in mid-flight? Or that they can spend several years underwater as larvae before emerging and transforming into winged adults? Dragonflies and damselflies are compelling to learn about, and we still have much to learn.
Some dragonflies migrate, much like birds and monarch butterflies. In fact, the longest-known insect migration in the world is undergone by a dragonfly called the wandering glider. In a migration that lasts for several generations, some populations of wandering glider travel 11,000 miles from India to southern Africa, twice the distance traveled by monarchs! We have a few species of migratory dragonflies right here in the Johnson Creek Watershed: common green darner, variegated meadowhawk, and black saddlebags. These were among the dragonflies studied by community scientists in 2016.
Want to sound fancy? Say “odonate!”
When talking about dragonflies and damselflies, we often just say “dragonflies” for shorthand. But this leaves out the poor damselflies, which are closely related. Odonate is a handy word that describes both. Scientists use a system called taxonomy to categorize organisms into groups based on shared characteristics: Each organism is placed into a kingdom, phylum, class, order, family, genus, and species. The Odonata group is a taxonomic order, with dragonflies in the suborder Anisoptera and damselflies in the suborder Zygoptera. So dragonflies and damselflies are a bit like cousins, and you can talk about both by using the special word odonate.
Odontos is a Greek word for tooth. Odonates are carnivorous as nymphs and adults, and the nymphs are characterized by toothed mandibles (jaws) at the end of a long, extendable mouth part. Adults have very large eyes; two pairs of transparent wings; and long, slender bodies. Both dragonflies and damselflies have an aquatic nymph, or larval, stage; they spend most of their lives (1-6 years) in this stage. They then undergo metamorphosis and emerge from the water as winged adults, mating, laying eggs, and dying soon afterwards.
Why are odonates useful to study?
Dragonflies and damselflies need aquatic environments, including still water like that of ponds, wetlands, or river backwaters; and the running water of large rivers. The assemblage of odonate species at a location can tell us a lot about that location, giving us clues about its water quality and ecosystem health. Tracking dragonflies and damselflies helps scientists develop watershed restoration goals.
From June to October 2016, nine dedicated volunteers surveyed two locations for odonates. The goal was to document odonate diversity, or the number of species found in the watershed. A second goal was to document abundance, or how many of each species might live in the watershed. Finally, we wanted to understand timing of species’ occurrence: When do adult dragonflies and damselflies first appear in our watershed? How might this compare with other local areas, or with other years?
Survey methods were developed by Celeste A. Searles Mazzacano of CASM Environmental. Celeste was our entomologist extraordinaire and scientific advisor on this project.
The more these surveys are repeated, the better we will understand these species. We will repeat the surveys in summer 2017; stay tuned for updates!
Interpreting the Graphs
In the graphs below, both survey locations are depicted: Westmoreland Park and Brookside Park. For each location, there is a graph showing cumulative abundance of all odonate species, followed by a second graph showing abundance of migratory species. Note that abundance is the number of individuals observed per species, and cumulative abundance is the sum of all individuals observed from all species.
Each dragonfly or damselfly is identified below by its scientific name. The scientific name is a combination of genus and species: Anax junius is in the genus Anax and the species junius. Each of these species has a common name as well, which is not shown on the graphs: Anax junius is called the common green darner.
Looking at the graphs shows us how odonates’ populations change over the course of the summer season. For example, Sympetrum corruptum, the variegated meadowhawk, has the longest season of any migratory species, being observed on both the first and last survey dates. Ischnura cervula, the Pacific forktail, was the earliest resident (i.e., non-migratory) species to emerge in the spring.
The migratory graphs show the abundance of the three migratory species and how their abundance changes over time. The seasonal graphs show cumulative non-migratory species and how their abundances change seasonally.