Late Sightings

This has been a weird year, as we all know, what with the pandemic affecting everything. I haven't gone out dragonflying nearly as much as in normal times, and I haven't been keeping up with this blog as much as I would like to either. I need to get back to doing some of these normal activities.

With that in mind, I've been visiting Little Cranberry Lake recently on nice sunny days. It's late in the season, but there are still three species of dragonflies that are out and active. One is the Autumn Meadowhawk.

The above photo shows a pair of Autumn Meadowhawks in tandem—that is, with the male attached to the female, though they are not in the wheel position. Notice the brighter red color in the male (top), and the tiny appendages at the tip of the female's abdomen (bottom). There are lots of these meadowhawks flying about and landing everywhere—including on people—but I haven't seen any of them laying eggs yet.

The other two dragonfly species are that are out and about are Paddle-tailed Darners and Shadow Darners. They are close cousins to one another, with very similar appearance and behavior. Let's take a look at some of the relevant field marks that help to identify them.

First, let's look at the Paddle-tailed Darner. Here is a male perched in the bushes.

What a beautiful creature. This species, remember, is the Happy-face Dragonfly. A few of the best field marks for this darner are illustrated below:

These field marks are the ones that are easiest to see in a perched individual, and they are quite definitive.

Next, let's take a look at the Shadow Darner. Here is a perched male:

The same field marks for this species are given below:

Notice the direct comparisons between the two species.

There is still a lot of activity going on, including egg laying in the darners, and more sunny days coming up. I look forward to additional days observing dragonflies before the end of the season.

The Whisperer Speaks!

This coming week, July 14-19, the International Congress of Odonatology meets in Austin Texas. Here's a poster for the event:



Here's an overview of the schedule of events:



The dragonfly whisperer will be there. In fact, I'll be giving two separate talks on Tuesday morning. The talks will focus on the two species seen in the following photo, the Paddle-tailed Darner (right) and the Autumn Meadowhawk (left):



The Paddle-tailed Darner, the Happy-face Dragonfly, is featured in the first talk, Spin-Dry Dragonflies: Nature's Fastest Spinners. This talk explores the splash-dunk/spin-dry suite of behaviors, and includes many slow-motion videos.

The second talk, Egg Laying in Autumn Meadowhawks, describes the unique egg-laying behavior of Autumn Meadowhawks. Again, slow-motion videos show the behavior in full detail.

Stop by and say hello if you're in attendance.

Cool Dragonflies

Well, we're nearing the end of dragonfly season. The days are getting shorter and colder, but there are still a few dragonflies out there. Yesterday, Betsy and I went to Little Cranberry Lake here in Anacortes to check out the action, and we saw quite a bit. Here's the lakeshore:



The temperature was 44 ˚F the entire time we were there, which was approximately from noon to 1:00 pm.

First, we saw quite a few Autumn Meadowhawks; mostly males, but a few females as well. We didn't see any egg laying activity, however.  Here are a few male Autumn Meadowhawks sitting on the bench near the shore:



This is a great place for them to bask in the sun. On the fence nearby a pair was in the wheel position:



Here are a couple males that at first glance appear to be in tandem, but in fact are just resting in close proximity:



Here's another male resting in the bushes just back from the shore:



We also saw darners, both Paddle-tailed Darners (Mr. Happy Face) and Shadow Darners. Here's a male Paddle-tailed Darner perched in the bushes:



For a size comparison, notice the small housefly at the 10 o'clock position.

Here's a close up of this individual, showing the happy face:



It's always wonderful to see this in person.

Finally, here's a female Shadow Darner:



A close-up look shows a bit of a happy face for her as well:



What a lovely November day at the lake.

Mount Baker

We went to Mount Baker yesterday. It was lovely, with temperatures in the mid 60s, beautiful scenery, and some fun birds and dragonflies. First, here's the view at Picture Lake, with Mount Shuksan (just over 9,000 ft in elevation) in the background:



Here's Mount Baker, with Betsy on the trail:



In this area we saw some Pine Siskins and Bohemian Waxwings. Here are a couple views of them:

Bohemian Waxwing (left), and Pine Siskin (right).

Notice the yellow tips on the primaries, and the two white splotches on the side of the wings. I was surprised to see Bohemian Waxwings, as opposed to Cedar Waxwings, and so was eBird—I had to file a rare species form for this sighting.

We also saw some darners, including one that did a series of three splash-dunks followed by a nicely visible spin-dry. We saw a couple different species flying by, but only one landed for us—a Paddle-tailed Darner (Mr. Happy-face).



What a beautiful day.

A Hovering Happy Face

One of the delights of the Fall season is that Paddle-tailed Darners are out in numbers. They can be seen patrolling the shoreline of lakes, ponds, and ditches. They also hover frequently, as they keep a close watch on their territory. Here's an example of the hovering behavior:

These dragonflies are beautiful, elegant fliers.

When hovering, they flap their wings out of phase—but not 180˚ out of phase. Recall that 180˚ out of phase means that the wings are moving in opposite directions—one goes down when the other goes up. What is observed in this video, however, is a phase difference between the wings of 100˚. With this phase difference, the wings flap in such a way that when one is at it's maximum downward position, the other is at its horizontal location.

For a specific example, when the hindwings flap downward, the forewings follow a short time later, so that when the hindwings are at the bottom of their stroke, the forewings are at the horizontal position on their way down. When the forewings are at their maximum down position, the hindwings are horizontal on their way up. Flapping out of phase like this improves efficiency, allowing for minimum energy expenditure as they hover.

In contrast, when dragonflies want to accelerate and reach maximum speed they flap their wings together. This is less efficient, and hence requires more energy, but the tradeoff is worth it when the desire is to get moving quickly to chase a rival or a potential mate.

A Real Head Turner

Darners use a variety of means to clean themselves. A particularly "splashy" method is the splash-dunk, followed by a spin-dry to dry off.

They also clean their eyes with their legs. The following video shows a Paddle-tailed Darner (the Happy-face Dragonfly) cleaning its eyes as it rests on its perch. Note the extreme flexibility of the eyes, which can rotate by at least 135˚.

Their eyes are beautiful, almost like small gemstones. Notice that the pseudopupils keep pointing toward the viewer as the head rotates, but that the "eyebrows" move with the eyes themselves. The eyebrows are actually pigment on the surface of the eyes, and are a permanent feature, visible even when the dragonflies dies.

Vitruvian Tattoo

I just had a request from a da Vinci/dragonfly enthusiast to use the Vitruvian Dragonfly, shown below, for a tattoo.



That should be interesting. I'm curious to see the final result.

The above is a polished piece of art by Sabine Deviche from my original concept shown below:



She also made the following full color version:



I think they're both fantastic.

You can find more of Sabine's wonderful artwork at her website:

http://devichedesigns.com/home

Auricles—Mystery Structure

The previous post, on the Columbia Clubtail, brought to mind an enigmatic set of structures of male dragonflies referred to as the auricles. The reason for the name is that the shape of auricles in some species is vaguely ear shaped. The function of the auricles is unknown at the moment, though the best guess is that they may assist the female as she tries to find the hookup point for mating.

Be that as it may, the auricles on some species are quite striking in shape and color. One such case is the Columbia Clubtail. The next two photos point out the auricles on a male Columbia Clubtail:





The auricles in this species are bright yellow, contrasting with the pruinose blue abdomen, and shaped like little tennis balls.

Here's another clubtail species, the Pacific Clubtail, which also has prominent yellow auricles.





Closely related to the clubtails is the Grappletail—also with prominent yellow auricles:





In darners, the auricles are more ear shaped, and not quite as prominent—though they do have a nice blue color. Here's an example in the Shadow Darner:





Here's another view, this time in a Paddle-tailed Darner:





Next is a view of the underside of dead Paddle-tailed Darner we found at Cranberry Lake.





Notice the little "hooks" along the edge of the auricles. What is their purpose?

In contrast, here is a similar view of a female darner, showing the lack of auricles:



All in all, the auricles are a mysterious feature of male dragonflies. Maybe one of these days we'll get to see these structures in action—that would be fun.

Wing Grabbing

Betsy and I just returned from Cranberry Lake, where we saw Hermit Thrushes, Varied Thrushes, and Red-breasted Thrushes (American Robins)—a three thrush day. The weather was calm, with temperatures in the mid 60s. A beautiful day at the lake.

We also saw lots of darners there—mostly the Happy-face Darner (Paddle-tailed Darner). Males were patrolling floating logs along the shore, looking for females. We were looking for them too, hoping to observe the behavior that occurs when males attach to females.

As I've described before, when a male darner lands on a female and attempts to attach the tip of his abdomen to the back of the female's head, part of the process involves the male grabbing the female's forewings and pulling them forward—until they're pointing straight ahead. Apparently this induces the female to lower her head, and expose the area where the male attaches, making it easier for him complete the process. 

We discovered this behavior at Beaver Pond in Winthrop, WA in a slow-motion video I took of a male attaching to a female. I published a description of the behavior in the Argia article below, and since then we're always on the lookout for another opportunity to see it. Well, today at the lake we got another chance, and I was able to get the following photo showing the male in the process of attaching to the female.

The female is on the bottom, and the male has his abdomen bent forward to bring the tip in contact with the back of the female's head. Notice also that the male is grabbing the female's forewing—on the left side, where we can see it—and is pulling it forward. The annotated version of the photo, shown below, indicates the key features.

The interesting thing about this photo is that I hadn't realized before that the male grabs the female's wing with all of his legs—not just the rear legs. This adds a new element to the behavior. When I watch the original video again (link below), I can now see that after the rear legs reach down and grab the wings, the middle and front legs join in and help in pulling the wings forward, and giving the female a "bear hug."

Here's a reprint of the Argia article I published describing this behavior for the first time.

Attaching in Tandem: The Role of “Wing Grabbing” and “Wing Pulling”

James S. Walker

One of the most interesting aspects of dragonfly behavior is the fact that they mate like no other creatures on Earth.  They begin by attaching in tandem, and from there they maneuver into the wheel position.  After mating, many species remain in tandem for quite some time as the eggs are laid.  Clearly, the tandem coupling is of crucial importance to dragonflies.

As a result, the actual process of attaching in tandem is of some interest.  It looks fairly straightforward, but the connection usually happens so quickly that few details can be discerned.  In this article, I present observations from a slow-motion video of darners attaching in tandem.  As we shall see, the male “grabs” the female’s forewings, and then “pulls” them forward to an extreme extent as it completes the attachment process.

Before the Attachment

The observations reported in this article come from a slow-motion video (1/4 speed) of a female Paddle-tailed Darner (Aeshna palmata) in the process of laying eggs on a floating log.  She was spending a lot of time probing the log for suitable places to lay eggs.  When satisfied with a location, she would visibly “bear down” as she made a cut into the wood.  

There were several males of the same species patrolling the area.  As I filmed the female, one of the males came swooping in and literally “pounced” on her – landing on her thorax.  Figure 1 shows the male just as he made contact with the female.  It was a sudden impact for the female, and the male immediately began to bend his abdomen downward and forward to bring his appendages toward the female’s head.  It took only 0.67 s to complete this action, and the male then proceeded with the attachment process in earnest.

Figure 1 A male darner makes first contact with a female on a log.

The Attachment Process

The process of attaching in tandem can be thought of as occurring in three phases.  The first phase appears to be a preliminary attachment, the second phase involves “grabbing” and “pulling” of the female’s forewings, and the third phase is the completion of a firm attachment to the female’s head.  In what follows, I flesh out the details of each of these phases.

Phase 1: Preliminary Oscillations (0.36 s) This phase begins when the male first brings his appendages into contact with the back of the female’s head.  After apparently latching onto the female’s head, the male then executes a series of 8 or 9 sideways oscillations of his abdomen with a frequency of roughly 60 Hz.  One might think this would complete the attachment, but there is more to come.

Phase 2: Wing Grabbing and Wing Pulling (0.60 s) At the beginning of phase 2, the female’s wings are in their normal position, as illustrated in Figure 2 (a).  The male now reaches his rear two legs downward, putting them between the forewings and hindwings of the female.  He then begins to “grab” the forewings, and “pull” them forward.  

When the forewings reach the position shown in Figure 2 (b), the legs are pulling quite hard on the forewings, causing a considerable distortion in their membranes.  In fact, this particular female had a tear in the middle of her left forewing, and the male’s rear leg fit nicely into the tear.  It appears that tears like this on a female’s forewing, which might ordinarily be chalked up to a bird attack, could instead be a sign of the rough handling that occurs during attachment.

Figure 2 Positions of the female’s wings during attachment.  (a) Normal position of wings.  (b) Wing grabbing begins, and forewings are pulled forward.  (c)  Final phase of wing pulling, resulting in forewings that point straight forward.

The male continues to pull the female’s forewing toward her head.  Eventually, the forewings are pointing directly forward, as in Figure 2 (c), and the plane of their membranes is vertical rather than horizontal.  The male now does a “bear hug” on the female, pressing her forewings firmly against her thorax.  The male holds the wings stationary against the thorax during this “bear hug”, and remains stationary himself, for about 0.22 s.

Phase 3: Final Oscillations (0.29 s) In phase 3, the male executes a series of roughly 15 side-to-side oscillations of his abdomen, like he did in phase 1.  The oscillations are again at about 60 Hz.  At the end of phase 3 the male has a good attachment, and he releases the female’s forewings.  He then begins to flap his wings.

After the Attachment

I mentioned that at the end of phase 3 the male begins to flap his wings.  I didn’t say he takes off, because in this case the female held on tightly to the log and prevented him from flying off with her, as shown in Figure 3.  The male tried and tried to dislodge the female – a couple times he even fell into the water briefly during his efforts.  After 7.5 s of futile attempts to takeoff, the male finally detached from the female and departed the scene.

Figure 3 After attachment the male darner tries to takeoff, but the female holds on to the log.

Additional Observations

After observing this “wing grabbing” and “wing pulling” behavior, I looked more carefully at other female darners that were potential mating partners for a roving male.  I have seen the same behavior in 3 additional cases now, clearly indicating that grabbing the forewing and pulling it forward are standard parts of their attachment process.

I haven’t had much of a chance to observe attachment in other families of dragonflies yet.  However, I looked back over earlier slow-motion videos to see if the behavior appeared in any of them.  In fact, one of my videos did show wing grabbing.  This involved a pair of Black Saddlebags (Tramea lacerata) that I filmed doing their egg-laying behavior of releasing the female, letting her drop to the water to lay an egg, and then immediately reattaching in flight.  The video showed clearly that the male grabbed the female’s forewings and pulled them forward as he reattached.  He pulled the forewings into the position shown in Figure 2 (b), which prevented them from flapping until attachment was accomplished.

I’ve also found a few published results that may bear some relation to the behavior reported here.  For example, Corbet reports that “… when a male Anax junius in tandem is attacked (bitten) by another male, the tandem male shakes its abdomen in a convulsive movement detectable to the human observer only when portrayed in slow motion” (Corbet, page 276).  This sounds similar to the oscillations observed in phase 1 and phase 3, though perhaps performed for a different reason.

In terms of interactions with the female’s wings, the following may be somewhat related.  Corbet states that when a male Ischnura graellsii detects a female he rushes at her, “… grasping and sometimes even biting her wing bases and simultaneously beating her wings with his abdomen …” (Corbet, page 485).  Similarly, he reports that a male Hemiphlebia mirabilis “… flew to a perched female and straddled her, holding her wings over her abdomen with all his legs for one or two minutes …”, (Corbet, page 485).  Though certainly quite different from the “wing grabbing” and “wing pulling” described here, these observations may be part of a larger repertoire of wing interactions during attachment.

Conclusions

It will be of some interest to see just how widespread the wing grabbing and wing pulling behavior is among dragonflies, and whether it is also done by damselflies, as suggested by the above observations.  

Some of the questions that can be addressed in future studies include:

•  Is wing grabbing done intentionally, or does the forewing just “get in the way” of the male’s hind legs?

•  If wing grabbing is intentional – and it looks that way in the video – what role does it play in attaining a solid attachment?  Does grabbing the forewings give the male a better grip on the female?  Does pulling on the wings trigger a response that helps to induce a female to mate?

These and many other questions can be addressed with additional observations over the years.  I know I’ll be looking more carefully at the attachment process in the dragonfly seasons to come.

Acknowledgements

I would like to thank Dennis Paulson and Betsy Walker for helpful conversations and feedback.

Literature Cited

Corbet, P. 1999.  Dragonflies: Behavior and Ecology of Odonata. Ithaca, New York: Cornell University Press.

Online Material

A male Paddle-tailed Darner (A. palmata) attaches to a female.

http://www.youtube.com/watch?v=p_ap7Aex9Y4

Black Saddlebags (T. lacerata) laying eggs and reattching.

http://www.youtube.com/watch?v=wukDS-1shAU

Beaver Pond

Yesterday, while the weather was still fantastic, Betsy and I took a day trip to Winthrop, WA. In particular, we went to the Beaver Pond near Sun Mountain Lodge—a great place for birding and dragonflying. Here's what the pond looked like yesterday:



Only after putting this photo on my computer did I realize there was a dragonfly in the picture—at the upper center. It's a male Happy-face Dragonfly, also known as the Paddle-tailed Darner. I know this because there were lots of them perching in the grass at this location.

It seems being a dragonfly whisperer has its perks!

Beaver Pond

Yesterday, Betsy and I drove over the mountains to Beaver Pond in Winthrop, WA for an afternoon of birding and dragonflying. We had a wonderful time—as usual—and even saw a moose at Rainy Pass on the way there.

Here's the location of Beaver Pond:



You park at the Chickadee Trailhead.

This is one of our favorite spots to visit each year. In fact, it's the location of one of my favorite photos of myself, which Betsy took along the shore of the pond! You can see some of the pond, the countryside, and a ponderosa pine in the background. BTW—The dragonfly on my finger is a Happy-face Dragonfly, aka Paddle-tailed Darner.



We saw lots of activity there. Here's a link to our eBird report:

http://ebird.org/ebird/view/checklist/S38218723

One of the first dragonflies we saw there was a beautiful Four-spotted Skimmer. It was so fresh and vibrant—much more colorful that you usually expect when thinking of this dragonfly.



We saw them mating—and you have to look quick to see it! They stay in the wheel position for only a couple seconds, and then the female immediately starts dipping and laying eggs. The male hovers overhead to guard her from intruders, which are usually other male Four-spotted Skimmers, but in this case also included male Paddle-tailed Darners. Why they were harassing the female skimmer I don't know.

Here's our list of odonates for the day:

Damselflies -- Northern/Boreal Bluet, Pacific Forktail, Northern Spreadwing

Dragonflies -- Blue-eyed Darner, Paddle-tailed Darner, Four-spotted Skimmer, Crimson-ringed Whiteface, Striped Meadowhawk

We also saw lots of fish jumping clear out of the water, apparently going after the damselflies that were skimming along just above the surface of the pond.

I hadn't expected to see splash-dunking and spin-drying, but was pleasantly surprised to see the behavior right from the moment we got there. Here's a list of the splash-dunk events we saw, in the order in which they occurred:

Splash-Dunks
1
2
2
3
2
2
6
2

We were watching this activity from the footbridge, and so many of the spin-drys occurred at eye level.

All in all, quite an interesting day.

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.