Wednesday, July 27, 2011

Tiger Spiketail


A well-shaded sandstone gorge in Ohio's Hocking Hills - perfect habitat for one of our most interesting - and rare - dragonflies, the tiger spiketail, Cordulegaster erronia. The small stream at the gorge's bottom essentially originates at the upper end of the photo, where a falls plunges over an impressive several story tall sandstone cliff. Overarching hemlock, birch and other trees insulate the stream from direct sunlight, keeping its waters cool. Hillside seeps add a constant infusion of cold groundwater, and decomposed sandstone forms plenty of saturated soft sandy margins to the stream.

I was in this gorge the other day looking for rare plants, specifically the tiny triangle grapefern, Botrychium lanceolatum. There is a small population here which I hadn't seen for about seven years, and I was able to refind it. This elfin fern only stands perhaps two inches in height - at least these plants - and one can scarcely see them in the gloom of the forest floor when standing upright.

But I got a real bonus on the trek to the fern.

While admiring a small population of rough sedge, Carex scabrata, near the stream's bank, a large black dragonfly prominently banded with yellow and sporting luminescent green eyes zipped by, low over the narrow stream. Tiger spiketail!

This is a fascinating insect; one of my favorites. It is a high-end predator and it probably wouldn't be far afield to compare the dragonfly to the sharp-shinned hawks that nest in this forest. Like the bird, spiketails require large blocks of intact forest, defend large territories, and are sensitive to disturbance such as logging. Plus, they just look VERY COOL. Ohio dragonfly expert Bob Glotzhober says a patrolling tiger spiketail resembles a miniature B-52 bomber. I like that analogy, and they do indeed suggest a small aircraft as they cruise low over the stream's waters, ranging from one end of their turf to the other.

My lucky spiketail day had just begun. After the dragonfly shot by, I readied my camera and prepared to settle in and hope for some shots. My experience with tiger spiketails is that they make systematic patrols, but it may take several minutes before the animal returns to a given spot and you've got to be ready or you'll miss it when it flashes by.

No worries. This spiketail turned out to be a female, and she selected a nice wet sandy flat about ten feet away to place her eggs. She shot in, hovered over the stream, turned to glare at the interloper - me - and then went about her business while I watched quietly from the shadows. Eventually I was able to creep into the center of the stream without disturbing her and make photos and watch the ovipositing process at remarkably close range.

Tiger spiketails place their eggs in permanently saturated sand in or along the margins of small order streams. "Place" might be putting it a bit delicately. Rather, the female violently lunges the tip of her abdomen and the ovipositor into the sand in the manner of a pogo-stick, making about one thrust per second. Forgive the less than crystal clear photos, but shooting rapidly moving dragonflies in deep shade is not the easiest task.

In the above photo, her abdomen tip is in the shallow water and making contact with the substrate. The water at this ovipositing site was not even an inch deep. She drilled in a lot of eggs, making many dozens of lunges in the short time I had to observe. Two other hikers stumbled along and made the stream crossing at this point, spooking the dragon and ending my study.

You can get a sense of the speed and violent force of the spiketail's thrusts in this photo. She singled out a small area - maybe a foot or so square - of apparently prime turf, and would concentrate her efforts in that spot.

video

This video should speak a thousand words about the tiger spiketail's ovipositing technique. It isn't the greatest video - my camera wanted to focus on the backdrop rather than the dragonfly - but she's clearly visible and you'll certainly see her style.

The tiger spiketail was a great bonus to an already highly productive field day.

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3 comments:

Scott said...

Great post and cool video, I spent over half a day chasing a male Tiger Spiketail last year and all I got was one green blur of a shot.

JSK said...

Agreed. Great post. The video is phenomenal

Heather said...

That's way cool, Jim! I'm glad you posted that video. If I were to come upon a dragon behaving like that, it would take me quite a while to come up with a reason for such behavior.