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Science & NatureWhat is That?What Is That … Transformation?

What Is That … Transformation?

Waddells

In these articles, we usually deal with several species following a theme.  However, this time we are taking a different approach to focus on a recently observed transformation of one individual from a dragonfly nymph into an adult.  Many insects go through interesting transformations during the stages of their life cycle, such as the commonly-known transformation of the monarch caterpillar, to chrysalis, to butterfly.  On June 1st of this spring, we were fortunate to observe and photograph the process of one ugly nymph transforming into a wonderous adult and we want to share this with you.

Observing this fascinating process is slow, slower than watching paint dry, so we are providing only a few highlights and the timeline for this transformation.  Most dragonfly nymphs mature to adulthood after one to three years living as voracious aquatic nymphs.  The transformation to adult typically begins early in the morning as the nymph leaves its long-time watery environment and emerges into the air on aquatic plants or other above-water, solid objects.  In the case of our intrepid nymph, it travelled overland some eight meters to find a spot and secure itself on the door of our boathouse.

When we headed out for our morning kayak around 6:00 a.m. we noticed the nymph hanging on the boathouse, pressed flat against the door.  On our return around 7:00a.m., we noted it was still there and had extended its legs so that the base of the abdomen was propped against the door and the head and thorax were extended outward.  Seeing this change in posture caused us to suspect ‘our’ nymph was in the process of transforming and so we decided to observe it for a while.

By 7:45 a.m., the back of the nymph’s thorax had split and the head, thorax, and legs of the young dragonfly, termed a teneral, had emerged.  The way the emerged portions hung backwards over the nymph case, it looked to us like the teneral might tumble out.  This did not happen as the new legs, once they were hardened and strong enough, were used to firmly hang on to the nymph case.

By 8:30 a.m., the teneral had pulled itself completely out of the case and was resting on it.  Blood was already pumping into its abdomen and wings in order to extend them to their full size.  Between each phase of these transformations, when the malleable young tissues have taken on their full adult size, the teneral takes some time for the various body parts to harden or ‘stiffen-up’.  The wings are barely discernable in the next photo.

By 9:10 a.m., the wings had grown to their full adult length.  Unfortunately, at this point we had to leave to run some errands and so did not see the wings extended in their bi-plane posture or see the first flight of  ‘our’ teneral.  When we returned from errands at 11:30 a.m., all that remained on our boat house door was the empty nymph case which is termed ‘exuviae’.  Experts we consulted indicated it is very difficult to identify dragonfly species at the nymph and teneral stages but were confident the transformed nymph was a species of emerald dragonfly.

A couple of days earlier we observed one of many perils dragonfly nymphs face during this miraculous transformation.  Numerous species of birds feed on nymphs as they emerge from the water just like this female red-winged blackbird.  One field guide noted “as much as 90 percent mortality has been observed in a population due to bird predation.”  This just goes to make ‘our’ nymph’s successful transformation even more amazing!

Now, over a month later the exuviae is still hanging on the boathouse door, a poignant reminder for us of this amazing transformation.

We relied on the three following field guides for details on the life cycle of dragonflies: Colin D. Jones, Andrea Kingsley, Peter Burke and Matt Holder’s The Dragonflies and Damselflies of Algonquin Provincial Park and the Surrounding Area; Kurt Mead’s Dragonflies of the North Woods; and, Dennis Paulson’s Dragonflies and Damselflies of the East.

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