Christmas Eve, 2016

The Happy-face Dragonfly wishes you a Merry Christmas:

Merry Christmas, 2016

Season's Greetings from the Happy-face Darner to the readers of "The Dragonfly Whisperer" blog.  Happy Holidays!

Splash-Dunk/Spin-Dry Analysis For 2011-2016

Here's an article I'm submitting for the next issue of Argia, the journal for the Dragonfly Society of the Americas.

As part of our dragonfly watching routine over the past several years, my wife Betsy and I have studied the splash-dunk/spin-dry suite of behaviors (Walker, 2014a). We enjoyed doing so again this year. The purpose of this paper is to update the results of our observations that now cover a total of 602 splash-dunk events and 13 spin-dry videos.

As a reminder, recall that splash-dunks are events where a dragonfly slams into the water at full speed to bathe (Walker, 2011), and a spin-dry is the subsequent 1,000 rpm spinning motion in mid flight to shed the water (Walker, 2014b). This is illustrated in Figure 1, which shows a typical 3 splash-dunk event, followed by a spin-dry. The dragonfly in this illustration is the Paddle-tailed Darner (Aeshna palmata), which is the species most commonly seen doing this behavior.

 

Figure 1 A typical splash-dunk/spin-dry event. The drawing is by Sabine Deviche (devichedesigns.com).

The 2016 season was memorable in a couple different ways. First, we noticed much less dragonfly activity than normal at our usual dragonfly locations in Anacortes, WA. For example, no American Emeralds (Cordulia shurtleffii) were seen at Cranberry Lake this year, though we usually see at least a few. In addition, there were fewer Four-spotted Skimmers (Libellula quadrimaculata) and Eight-spotted Simmers (Libellula forensis) than in previous years.

On a more positive note, the other interesting occurrence this season was a particularly impressive spin-dry performed by an Eight-spotted Skimmer, like the one shown in Figure 2. This occurred in mid summer, when we were observing dragonflies in eastern Washington at the Quincy Lakes complex of lakes and beaver ponds near Quincy, WA. At one point we were looking down from a hillside at a small beaver pond. The water was dark, and we immediately saw a brilliant Eight-spotted Skimmer take flight from the shoreline. It flew out over the water, did a series of three splash-dunks, gained a bit of altitude, and then did a spectacular head-over-heels spin-dry with its flashy black-and-white wings spinning rapidly. It was quite a sight to behold, especially when compared to the much more common, but less showy, spin-dry of a darner with its clear wings.

 

Figure 2 A male Eight-spotted Skimmer showing off its flashy wings.

The Number of Splash-Dunks per Event

Whenever we see a dragonfly initiate a splash-dunk event, we count the number of splash-dunks it performs before it rises to do a spin-dry. This is often just a single splash-dunk, but in many cases the event extends to a series of several splash-dunks in a row. The maximum number of splash-dunks we’ve seen in any one event is 8, as described in the case of the constipated dragonfly (Walker, 2013).

Figure 3 shows the results of our observations for the six dragonfly seasons from 2011 to 2016. In a normal year we see an average of 115 events, but this year, with its low activity level, we saw only 25 events. Still, the total number of events represented in Figure 3 is 602. Notice the almost exponential falloff as the number of splash-dunks increases, with a noticeable “shoulder” at 3 splash-dunks. This feature has persisted for several years now (Walker, 2014a), indicating an unexpected preference for events with this number of splash-dunks.

 

Figure 3 Cumulative splash-dunk data for the 602 splash-dunk events observed during the years 2011 to 2016.

The average number of splash-dunks per event is 2.31. This result is unchanged over the last three years—a significant finding, considering that the statistics are derived from hundreds of observations.

Temporal Distribution of Splash-Dunking

Another important aspect of splash-dunk behavior is the time of year in which it occurs. We record the date of all the splash-dunks we record, and the month-by-month result is shown in Figure 4. Notice the large peak in September, when more than half of all events are observed.

 

Figure 4 Temporal distribution of 602 splash-dunk events from 2011-2016.

Part of the reason for the September peak is that this is also the peak month for the flight season of the Paddle-tailed Darner, which is shown in Figure 5. Notice the similarity between the chances of seeing a Paddle-tailed Darner and the chances of seeing a splash-dunk. The main discrepancy is that fewer splash-dunks are seen in July and August than one might expect on the basis of the flight season.

 

Figure 5 Flight season for the Paddle-tailed Darner.

The flight season of the Shadow Darner (Aeshna umbrosa) is shown in Figure 6. Again, the flight-season and splash-dunk distributions are similar, but notice that more splash-dunks would be expected in October and November if the Shadow Darner were the primary splash-dunker. It seems that the actual splash-dunk distribution is roughly an average of what one might expect from these two darners.

 

Figure 6 Flight season for the Shadow Darner.

One final comparison is shown in Figure 7. This is the flight season of the Blue-eyed Darner (Rhionaeschna multicolor), which is also seen to splash-dunk on occasion. Notice the very different temporal distribution for this species compared with the distribution of splash-dunks.

 

Figure 7 Flight season of the Blue-eyed Darner.

Another reason for a lot of splash-dunking in the Fall may be that this is also the season when spider webs carrying young spiders are frequently drifting through the air. It is not uncommon to see darners speeding by in September with a spider web trailing from their abdomen. This is quite possibly the reason for many of the splash-dunks we see.

Splash-Dunk Species

As mentioned above, most of the splash-dunks we observe are performed by Paddle-tailed Darners. We also see Shadow Darners doing splash-dunks, though they seem to hit the water with less force than do the Paddle-tailed Darners. A comparison between these two species is presented in Figure 8. The two darners on the left are Shadow Darners, and the one on the right is a Paddle-tailed Darner.

 

Figure 8 A comparison between Shadow Darners (the two on the left) and a Paddle-tailed Darner. These are “free range” dragonflies that have been “whispered” onto my fingers.

We occasionally see splash-dunks performed by the following darners as well:

California Darner (Rhionaeschna californica)

Blue-eyed Darner (Rhionaeschna multicolor)

Common Green Darner (Anax junius)

Species from other families of dragonflies have also been observed to splash-dunk—like the Eight-spotted Skimmer mentioned above—though usually just in isolated incidents. These species are as follows:

Four-spotted Skimmer (Libellula quadrimaculata)

Eight-spotted Skimmer (Libellula forensis)

Western Pondhawk (Erythemis collocata)

Autumn Meadowhawk (Sympetrum vicinum)

Blue Dasher (Pachydiplax longipennis)

The Autumn Meadowhawk is notable on this list for being the only species we have observed so far to do a spin-dry while attached in tandem. Their tandem spin-dry was very slow, and lasted for only a couple rotations.

Spin-Dry Statistics—The Fastest Rotating Animal

A fitting end to a series of splash-dunks is an invigorating spin-dry to shed the water. Data is harder to obtain for a spin-dry than for a series of splash-dunks because the spins happen so quickly. When I get a good slow-motion video of a spin-dry, however, I can then analyze it in detail. This season I added a 13^th slow-motion spin-dry video to my collection, giving just that much more specific information on the behavior.

Figure 9 shows this 13^th darner performing a splash-dunk—one of 6 it did in this event. It then gained some altitude (perhaps 3 to 5 feet) and did the spin-dry shown in Figure 10. This video was detailed enough that I could count the number of frames (filmed at 240 frames per second) corresponding to each individual rotation. As a result, we know that the spin-dry consisted of 7 revolutions, lasted 0.458 seconds, and had a maximum spin rate of 1,200 rpm.

 

Figure 9 A darner approaches the surface of Cranberry Lake (left), and then plows into it (center), sending up a plume of droplets as it comes to a complete stop. It then emerges from the water to do it all over again (right).

 

Figure 10 The darner from Figure 9 in the process of doing a spin-dry. It is surrounded by a fine halo of water droplets shed by the 1,200-rpm rotation.

Figure 11 collects the results from 13 slow-motion videos of the spin-dry behavior. It shows the spin rate for each event, along with a red line indicating the average value. As can be seen, 1,000 rpm is a good round-figure to characterize spin-drying in dragonflies—the fastest known rotational motion of any animal.

 

Figure 11 Spin rate for 13 different darners doing a spin-dry. The red line indicates an average value just more than 1,000 rpm.

To be specific, the data from these 13 videos gives the following numerical results:

Number of rotations in a spin-dry = 5.85 ± 1.18 revolutions

Time spent spinning = 0.443 ± 0.062 seconds

Maximum spin rate = 1,060 ± 207 rpm

Finally, the centripetal acceleration associated with a spin-dry is quite large—certainly more than enough to shed water. The angular speed is w = 1,200 rpm = 111 rad/s, and the corresponding centripetal acceleration is rw², where r is the radius of the spinning object in meters and w is the angular speed in rad/s (Walker, 2016). It’s hard to estimate r, but a reasonable value for a 70-mm darner is somewhere between r = 0.01 m and r = 0.03 m, giving an acceleration of 120 m/s² to 370 m/s². Thus, the spin-dry produces an acceleration ranging from about 10g to 40g, where g = 9.81 m/s² is the acceleration due to gravity. This is quite an impressive “g force” for any organism to endure—and they don’t even get dizzy.

Future observations may yield videos of other types of dragonflies doing a spin-dry. When this occurs, the comparison with the spin-dry of darners will be of great interest.

Acknowledgements

I would like to thank Betsy Walker for help collecting the data presented here.

Literature Cited

Walker, J. S. 2011.  Splash-Dunk Analysis, 2011.  Argia 23(4): 29-30.

Walker, J. S. 2013.  The Strange Case of the Constipated Darner.  Argia 25(3): 29-30.

Walker, J. S. 2014a.  Splash-Dunk Analysis for 2011-2014.  Argia 26(4): 32-33.

Walker, J. S. 2014b.  Life at 1,000 RPM.  Argia 26(2): 11-13.

Walker, J. S. 2016.  Physics, 5^th edition.  Pearson Addison-Wesley.

Senior College Dragonfly Class in Anacortes

Hi Everyone,

Betsy and I had a great time presenting the Dragonfly Class for the Senior College in Anacortes. We finished yesterday afternoon with a discussion of Splash-Dunking and Spin-Drying.

We also showed a trailer for the Happy-face Dragonfly movie. Some of you were hoping to see it again, and possibly share it with friends, so here's a link to it on YouTube:

Happy-face Trailer

In addition, here's a link to the Dragonfly Whisperer Channel on YouTube:

Dragonfly Whisperer Channel

You will find many more dragonfly videos there, including many that were presented in class.

Thanks again for your enthusiastic participation, and we hope to see you next summer on a dragonfly field trip.

Happy Dragonflying!

It's Still Dragonfly Season!!!

Well, when the sun comes out, so do the dragonflies. Betsy and I went to Cranberry Lake today around noon, and were greeted by a nice group of dragonflies—even though it was quite breezy. The temperature was delightfully mild too; in the mid 60s.

We immediately saw lots of Autumn Meadowhawks. This species has a beautiful red color, and is so friendly that they land on you if you stay put for more than half a minute or so. Here are a couple that visited with us:

We also saw a single Variegated Meadowhawk, which we've never seen at Cranberry Lake before. This species can pop up just about anywhere, just about any time of the year:

We also saw the usual darners for this time of year—the Shadow Darner and the Paddle-tailed Darner. Here's a Paddle-tailed Darner, resting in the bushes, soaking up the sun:

Here's another:

What a lovely day at the lake, made even more so by the presence of our friendly neighborhood dragonflies.

The Whisperer Speaks!

I'll be giving a talk tomorrow at the Garden Club on Samish Island. Should be a lot of fun.

Here's the handout for the talk:

See you there tomorrow!

Happy Tenth Birthday

An important day in my development as a Dragonfly Whisperer was October 22, 2006, when I took the first photo of the Happy-face Dragonfly at Cranberry Lake in Anacortes, WA.  I was just trying to get a good macro shot of the Paddle-tailed Darner's head, and had no idea what a delightful happy face it has until I brought the photo home and viewed at it on my computer.  That was ten years ago, and was the impetus for my continuing interest in dragonflies.

Friendly Dragonflies

This is the time of year when two of my favorite dragonflies are out in force – the Paddle-tailed Darner (Happy-face Dragonfly), and the Autumn Meadowhawk.  In the following picture I whispered a Happy-face Dragonfly onto my finger, and in the meantime a few Autumn Meadowhawks decided to join me and land on my leg.  Such friendly dragonflies!

It's wonderful to see these dragonflies together in the same picture – especially when the Happy-face Dragonfly likes to prey on the Autumn Meadowhawks.  It's doubtful the darner sees the perched Autumn Meadowhawks as potential prey items, since it likes to hunt flying prey on the wing, but it's interesting to have the lion lay down with the lambs in any case.

Latest Version of the Vitruvian Dragonfly

Here's the latest version of da Vinci's classic illustration:

I just love this dragonfly, the Paddle-tailed Darner, aka the Happy-face Dragonfly.  Such beautiulf colors and patterns.

A New Vitruvian Dragonfly

In the past, I put together a stick figure version of the Vitruvian Man – only in my case it was done as a dragonfly.

It's based on the Happy-face Dragonfly, also known as the Paddle-tailed Darner, and is taken from a photo, ensuring that the proportions are correct.

I recently commissioned a wonderful artist, Sabine Deviche, to do a professional version of the Vitruvian Dragonfly.  Here's the result, which is just beautiful:

I love the details in the wings, and everything else about the drawing as well.  It has a very classic feel to it.

"I Looked For It"

This is a repost from some time ago.  I was reminded of it by seeing Jeremy Brett's version of The Adventure of the Dancing Men on PBS a few days ago.  It's an excellent adventure – other than the fact that his client dies!

One of my favorite literary characters is Sherlock Holmes.  I've often wondered what it would have been like if Holmes had taken up birdwatching instead of beekeeping. A birder with the sharp observing skills of Sherlock Holmes would be something to behold.

Sherlock Holmes in the field.  Looking for birds?  Dragonflies?

I can just imagine an exchange between Holmes and Watson going something like this:

Watson:  Look Holmes, a Hutton's Vireo.
Holmes:  If you look closely, Watson, I think you will find that it is actually a Ruby-crowned Kinglet.
Watson:  Why do you say that Holmes?
Holmes:  Elementary my dear Watson.  Notice the yellow feet, the delicate bill, and the light wing bar with a distinct black border, all sure signs of a kinglet.
Watson: By Jove, Holmes, you're right.  I just saw it flash its ruby crown.

The other day I had a chance to repeat a famous line from the Holmes canon in the context of dragonflying.  It was fun.  The line, basically, is "I looked for it," and it occurs in a couple Sherlock Holmes stories.

One example is in Silver Blaze, which is actually more famous for the following exchange:

Gregory (official police detective): "Is there any other point to which you would wish to draw my attention?"

Holmes: "To the curious incident of the dog in the night-time."

Gregory: "The dog did nothing in the night-time."

Holmes: "That was the curious incident."

Later in the story, Holmes lies on the ground and searches through the mud, finally finding a crucial clue – a small match.

Holmes on the prowl for clues.

"I cannot think how I came to overlook it," said the Inspector, with an expression of annoyance.

"It was invisible, buried in the mud. I only saw it because I was looking for it."

Ah, he looked for it.  Exactly.

A similar exchange occurs in The Adventure of the Dancing Men.  A key part of that adventure is a coded message written with dancing men, as follows:

At one point Holmes and a police inspector are investigating the scene of the crime when the following conversation ensues:

“… there are still four cartridges in the revolver," said the inspector. "Two have been fired and two wounds inflicted, so each bullet can be accounted for."


“So it would seem,” said Holmes. “Perhaps you can account also for the bullet which has so obviously struck the edge of the window?”


He had turned suddenly, and his long, thin finger was pointing to a hole which had been drilled right through the lower window-sash, about an inch above the bottom.


“By George!” cried the inspector. “How ever did you see that?”


“I looked for it.”


Indeed.

In my case, I was dragonflying at Cranberry Lake, when I saw a Happy-face Dragonfly in the bushes.  It looked like this:

A male Happy-face Darner smiling up at me.

A man walking by saw me looking intently at the bushes.  He stopped and asked, "What do you have there?"

"A dragonfly," I replied.

"Oh, really? Where is it?"

"Right here," I said, pointing into the bushes.  It took some time to help him find it in the tangle of branches.

When he finally found it he stepped back, looked at me, and said, "How did you ever find it there?"

"I looked for it," I said.

Sun Mountain Lodge

Betsy and I just got back from a few days at Sun Mountain Lodge.  It's one of our favorite places to visit.



The views from the grounds of the lodge are spectacular:





Just down the hill from the lodge is Beaver Pond, a wonderful place to enjoy nature.  Here's what it looks like at the pond:



This is the view from the footbridge at one end of the pond.  The trail that goes around the pond is lined with ponderosa pines.



The odonate activity at the pond was lively, as usual.  Paddle-tailed Darners, the familiar Happy-face Dragonfly, were seen flying back and forth over the pond constantly.  Here's a shot of one in flight:



This shot shows the two, side-by-side, paddle-shaped upper appendages at the tip of the abdomen – which overlap in this view, giving the impression of a single paddle.  The fact that there are two paddles is indicated by the two downward-pointing spines, one on each paddle.  You can also see the blue spots on the last (10th) segment of the abdomen, as well as the prominent eyebrow on the eye.  Notice as well that the front two legs are tucked up behind the eyes, in their usual flight position.

We also saw many damselflies at Beaver Pond, including this lovely Northern Spreadwing:



In addition, we encountered many Boreal Bluets, like this male perched on a leaf:



We had hoped to see some Northern Bluets, which are virtually identical to the Boreal Bluet, but all we looked at carefully turned out to be the Boreal Bluet.  It seems the two species generally don't mix, but tend have their own separate territories.

Lower Crab Creek: Twelve-spotted Skimmer

We had a great time visiting Lower Crab Creek a couple weeks ago.  Here's what it looks like there.



One of the other species we enjoyed at Lower Crab Creek was the Twelve-spotted Skimmer.  Here's an example:



This species looks a lot like the Eight-spotted Skimmer but, as one might imagine, it has four extra dark spots – one at the tip of each of its long thin wings.

This is a young male, and it still shows yellow striping along the edges of the abdomen.  As it matures, the abdomen will become pruinose whitish-blue, and the yellow stripes will be hard, if not impossible, to see.  The yellow stripes remain visible at all ages in females.

Finally, notice that the front two legs are folded up and tucked behind the head.  You can see those legs just behind the eyes – in fact, the small white spots you see there are actually the "knees" of the legs; that is, the folded joints in the middle of the leg.

Butchart Gardens

A couple days ago, Betsy and I visited Butchart Gardens on the way back from our cruise to Alaska.



It's a lovely place, and the weather was perfect.  Flowers everywhere, of course.







Many darners were flying over the open grassy lawns, but no other odonates were seen for a while – until we came to the "Star Fountain," shown above.  There we saw lots of Tule Bluets, including one that liked to perch on the begonias:





Notice the almost equal-width bands of black and blue on the abdomen, with the black bands actually a bit wider than the blue ones.  The Northern and Boreal Bluets differ in having mostly blue on the abdomen, with small black rings separating them.

In addition, we saw a darner fly in and land on one of the "frogs" that shoots out streams of water.  Here it is:



It's clear that this is a female, due to its overall brownish and greenish color, and the expanded tip of the abdomen that holds the ovipositor.  Females are generally a bit more difficult to identify than males, but in this case the identification was easy.  Notice the small "bump" – or tubercle – below segment 1 of the abdomen.  Here's a better view of the bump:



The interesting thing about this bump is that it's a distinctive field mark for the female Blue-eyed Darner.  None of the other mosaic darners in our area have this bump.  It's a good field mark to look for, though it's not always as easily seen as it is in this view.