Wednesday, May 4, 2011

A Dragonfly Emergence Sequence

While on the southern coast of Oregon last weekend I checked a pond in Bandon for odonates to see what was flying. There were lots of Pacific Forktails (Ischnura cervula) and a few Tule Bluets (Enallagma carunculatum) flying, but no dragonflies. However, I did come across two American Emeralds (Cordulia shurtleffii) that were in the process of emerging. Below is a sequence of shots of one of them which I took periodically while I also looked for nymphs in the water. I included the time stamp in the upper right corner (hh:mm:ss), so you can see how much time elapsed between each shot.


Emergence was well underway by the time I found this individual. The nymphal skin split over the
top of the thorax where the head and thorax squeezed out. The legs and compressed wings are
exposed. The white threads are tracheal linings. They remain attached to the exuvia and are pulled
out as the thorax is exposed to open up the spiracles and facilitate the transition to air breathing. At
this point she is only supported by her abdomen which is partly still in the exuvia. This yogic
“bent over backwards” position is common among dragonflies at this stage of emergence.

While I was distracted, she used her now hardened legs to pull the rest of her abdomen out of the exuvia.
Wing expansion is well underway.




The wings are just about fully expanded and they are losing some of their opaqueness.

The abdomen is lengthening more noticeably now.

The wings are much clearer and the abdomen is just about there. Parts of the thorax are starting to turn
metallic green, particularly along the sutures.

I wasn’t able to stick around much longer, so I carefully transferred her to another perch and collected the
exuvia. During emergence and for a short time immediately after is the only time that you’ll see a dragonfly
perch with its wings closed over the thorax/abdomen like you see here. I imagine she was here for another
half hour or more before taking her maiden flight.

This was the first winged dragonfly that I’ve seen this season—in other words an adult, and it seems particularly fitting that she was in the process of emerging when I found her. I’m ready for more . . .

5 comments:

  1. Great series! Interesting to see how fast the wings and abdomen expand.

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  2. Extraordinary series! Glad you could stay around for an hour or so to record it. And share it.
    Thanks!

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  3. What are the white, thread-like filaments in this sequence?

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  4. @Redshift Those are the tracheal linings. They stay attached to the exuvia, so they are pulled out of the trachea during emergence. This opens them up for air breathing.

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