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.

Latest Dragonfly—So Far!

We keep setting new records for the latest flight date of the season. A new record for the Shadow Darner was set just a few days ago, and yesterday a new record for any kind of dragonfly in our area was set with the observation of an Autumn Meadowhawk on December 9, 2019.

The temperature was a fairly mild 42 ˚F, and it was nice and sunny, with just a slight breeze. We checked all the likely spots—the benches, the fence, the face of the dam—but came up empty. It seemed that the recent string of cloudy and rainy days had terminated the dragonfly season in Anacortes. But then I noticed some motion on the trunk of a tree far back from the shore. Looking carefully, I spotted a male (of course) Autumn Meadowhawk basking in the sun. Here's a photo of him:



Getting a bit closer we can see him in detail:



I say 'of course' when referring to the fact that we saw a male, because we haven't seen a female for several weeks. It really seems that at the end of the season the population becomes asymmetric, with males far outnumbering females. This applies not only to the Autumn Meadowhawk, but to the darners we see at Little Cranberry Lake as well.

We returned home and enjoyed a lovely sunset:



The sunset was all the more satisfying knowing one of our friendly dragonflies was still alive and well at Little Cranberry Lake.

A Late Darner—Setting A New Record

I always keep track of the first and last flight dates for the various species in our area. Last week, November 22 to be precise, a Shadow Darner set a new record for the late date for that species. It was a cool day, only 41 ˚F, but nice and sunny. We saw only a single individual, a male, and it was flying near the treetops catching prey, landing for a while, then taking flight and catching more prey, and so on.

A week or so before that we had similar interactions with a Shadow Darner. We were at Little Cranberry Lake on a field trip for my dragonfly class. Here's what the lake looked like that day:



A Shadow Darner was seen perched in the bushes:

Notice the wide front stripes on the thorax, and the black tenth segment on the abdomen. I whispered it onto my finger to share with the group:



It has a bit of a happy-face appearance. In fact, here's one I saw later perched on the dam, giving a good view of its happy face:



Getting back to the one on my finger, as I was holding it Autumn Meadowhawks came in to land on me too:



Everyone had a good time taking pictures of the dragonflies—it was a true "Dragonfly Whisperer" experience for the class!

Late Dragonflies

Well, it's still dragonfly season!

Yesterday we went to Little Cranberry Lake here in Anacortes. We weren't expecting much, since it had been rainy the last couple days. But the clouds cleared off by mid morning, and at noon it was a nice sunny day, with a temperature of 52 ˚F, so we decided to check out the lake just in case. I'm glad we did.

First, we saw a Tule Bluet, the first damselfly we've seen at the lake since October 9. Here it is:



Next, we saw Autumn Meadowhawks all over the place, with several tandem pairs laying eggs:



They would lay eggs for a bit, in their typical Autumn Meadowhawk way (see my field guide for more details), then they would land on the shore to rest in the sun. Often, this meant that they would land on me, which is always a treat!



Darners were also present—specifically, Shadow Darners. A female was laying eggs on the shoreline for quite some time, and then a male came along and attached to her. He tried to takeoff with her to mate, but she resisted. You can see the male attaching and attempting to takeoff in the pictures below:





Eventually the male gave up, and they separated. The female then landed on the shore to rest:



All in all, quite an active day, especially for so late in the year.

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.

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.

Late Season Observations

Yesterday, Betsy and I went to Cranberry Lake. It was a beautiful, sunny, calm day, with temperatures in the low 50s. It's kind of late to be looking for dragonflies, but we're nothing if not optimistic.

The most common dragonfly we saw was the Autumn Meadowhawk—as one might expect. There were several perched in the sun on the concrete dam. Here's an example:



Notice the hamules under segment 2 of the abdomen, showing that this is a male—which is also quite evident from its bright red color. Here's another view:



We saw one of these guys do a splash-dunk, as well. It will probably be the last splash-dunk of the season.

We also saw a few Shadow Darners, flying along the shore and perched in the bushes. Here's an example of this species:



Notice the broad blue stripe on the top of segment 2 of the abdomen, plus the broad front stripes on the thorax and the lack of blue on segment 10.

You can find more information about both of these species in Common Dragonflies and Damselflies of the Pacific Coast.

Happy Happy Happy-Face!

Over the years I've taken literally thousands of photos of the Happy-face Draongfly (aka, the Paddle-tailed Darner).  Here's a small sampling:

The two photos on the bottom right of the grid were taken on the deck in our backyard.  All of the rest were taken at Cranberry Lake, where we see the Happy-face Dragonfly all the time in the late summer and early fall.

The photo in the center is still my favorite.  In fact, it was the first one I ever took of the Happy-face Dragonfly, on October 22, 2006.  I reached into the bushes with my camera and took a shot of a dragonfly perched there without even looking at the viewfinder.  When I loaded the photo onto my computer at home I was amazed, and I called to Betsy.  "Take a look," I said, "this dragonfly has a happy-face!"  This discovery launched my interest in dragonflies, which has given me great pleasure ever since.

The following quote from Henri Poincaré summarizes my feelings about science and nature quite well.

I might add to this thought, however, that the scientist also delights in nature because it is infinitely intriguing and surprising – just take the Happy-face as an example!

I'm nearing completion of my dragonfly field guide, Common Dragonflies and Damselflies of the Pacific Coast, and one of its features will be spreads on things I've discovered in my days as a dragonflier, like the Happy-face Dragonfly, Splash-Dunk/Spin-Dry, Autumn Meadowhawks egg laying behavior, etc.

Below is the first draft of the left side of a spread on the Happy-face Dragonfly. It provides a view of a variety of Happy-face individuals, showing the variation in their facial features.



On the right side of the spread I compare the Happy-face of the Paddle-tailed Darner with the face of other species of darner. The Shadow and Variable Darners are in the same genus (Aeshna) as the Paddle-tailed Darner, and their faces are quite similar—including eyebrows that are actually pigments on the eyes. On the other hand, the California and Blue-eyed Darners are in a different genus (Rhionaeschna) and their eyes lack the eyebrows, giving them quite a different look.



It's fortunate that my first face picture of a dragonfly's face was of a Paddle-tailed Darner, since it has the most dramatic "Happy-face" look.

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.