Saturday, December 23, 2017

Happy Holidays!!

Season's Greetings and Happy Holidays!

Special greetings from the Happy-face Dragonfly:

To help us all get in the Christmas spirit, here's a physics problem from Walker Physics involving Santa:

The situation can be visualized as follows:

And now for the calculation:

Here's a bit of insight into the results:

Ah, nothing like a physics calculation to add to the enjoyment of a day.

Merry Christmas!

By the way, Amazon is offering my new field guide, Common Dragonflies and Damselflies of the Pacific Coast, at a very good price. Here's the link:

Tuesday, November 28, 2017

Species Spotlight: California Spreadwing

The next species in the "spotlight" is the California Spreadwing, the largest damselfly in the Puget Sound area. It is so large, in fact, that on the wing it can look like a female meadowhawk.

This species was first seen in our area at Magnuson Park in Seattle, but since then it has been found at a number of other Puget Sound locations as well. It is more common in western Oregon and much of California. Here's the range map for this species:

Definitely a western species.

In addition to being conspicuously large, the California Spreadwing is easily identifiable by its overall brown color, with pale markings on the sides of the thorax. In particular, there is one prominent light-colored side stripe with contrasting dark borders that is an excellent field mark for this species. It also has pale rings along the length of the abdomen. You can see these features clearly below:

The female looks much the same as the male, with the same side stripes on the thorax. Her abdomen is rather stocky, however, and it has a prominent ovipositor at the tip. In the following photo a female is being held by a male, who grabs her by the front of the thorax. Male dragonflies hold the females by the back of the head, but the head is so small in damselflies that it is better to grab the female by her thorax.

This is an interesting damselfly, and one that is easy to spot due to its size.

Read more about this and other west coast odonates in my field guide:

Monday, November 20, 2017

Splash-Dunk Analysis, 2011-2017

As in past years, Betsy and I recorded all of our observations of dragonflies splash-dunking and spin-drying. This was a particularly slow year, as far as dragonfly activity goes, and for only the second time since we started in 2011 we had fewer than 100 Events—86 in fact.

Before continuing, let's make it clear what is meant by an "Event." For our purposes, an Event begins when a dragonfly hits the water in a splash-dunk. If the dragonfly rises after the splash-dunk and performs a spin-dry, then that was a one-splash-dunk Event. If the dragonfly does two splash-dunks, then rises for a spin-dry, it's a two-splash-dunk Event, and so on. Each time we see an Event beginning, we keep count of the number of splash-dunks before the spin-dry.

Secondly, let's give a reminder why the dragonflies are splash-dunking in the first place: They are bathing. When dragonflies perch they hold their wings straight out, and they cannot clean them. The wings collect various types of debris, and the way to clean them is to plunge into the water one or more times.

Here are the results for splash-dunk events in 2017:

Splash-Dunk Events for 2017. Total number of Events is 86; average number of splash-dunks per Event is 2.41.

This is a typical distribution, with the number of splash-dunks per event ranging from 1 to 7. Compare this with the cumulative results for 2011-2017:

Splash-Dunk Events for 2011-2017. Total number of Events is 688; average number of splash-dunks per Event is 2.32.

These are the results from observations of 688 splash-dunk Events. The average number of splash-dunks per Event is 2.32. Notice that more Events have just a single splash-dunk than any other number. In addition, the record number of splash-dunks in an Event is still 8—the number of splash-dunks in the famous event associated with the constipated darner. You can read details about the constipated darner at the following link:

Each year we see that there seems to be a bit of an excess in the number of Events around 3 and 4 splash-dunks. Let's look at this a bit more carefully. We begin with an exponential fit to the data:

The red dots are the data points, and the blue line is an exponential fit of the form a Exp[–bx], with the parameters a and b taking on the values a = 425 Events and b = 0.488 Events/splash-dunk. This shows clearly that the data is generally exponential in its fall-off, but with an excess of Events at 3 and 4. This has been a significant feature of the data each year.

The exponential fall off implies that each splash-dunk is an independent occurrence; that is, after each splash-dunk there is a certain probability that the dragonfly will do another splash-dunk independent of how many splash-dunks it has already performed. For the most part, this seems to be a valid description of the splash-dunk behavior. For some reason, however, there is a greater probability that a dragonfly will perform 3 or 4 splash-dunks. Perhaps fewer than 3 splash-dunks is usually not enough to clean the dragonfly, whereas more than 4 splash-dunks starts to get tiring, making the 3 to 4 range sort of a "sweet spot" for the dragonflies.

Tuesday, November 14, 2017

Swarming Meadowhawks

The Autumn Meadowhawks are the last dragonflies flying in our area. I thought I would re-post a description of a swarm of Autumn Meadowhawks that I encountered at Cranberry Lake 6 years ago. Here it is:

Recent reports of mass gatherings of dragonflies make it seem there is “something in the air” when it comes to events like these.  Large numbers of baskettails have been observed in Canada, and a large gathering of Striped Meadowhawks was recently seen in Oregon.

In my case, the dragonflies involved were Autumn Meadowhawks.  These friendly dragonflies, which like to land on people, are a common sight at Cranberry Lake in Anacortes, Washington late in the season.

Betsy experiences a red dragonfly on the shoulder, and a second one on her hat.  Both dragonflies are male Autumn Meadowhawks, the friendliest dragonfly we know.

Autumn Meadowhawks are well described by a famous haiku:

Red dragonfly on my shoulder,
Calls me his friend.
Autumn has arrived.

I’ve often had them “on my shoulder,” but last autumn I had them covering my entire body – literally from head to toe.  Here’s what happened.

I went to Cranberry Lake on November 9, 2011 to observe the dragonfly activity.  The weather was sunny and calm, with an air temperature of 57 ˚F.  On other similar days I would observe about a dozen Autumn Meadowhawks and half a dozen Shadow Darners.  On this day, however, I immediately realized something was different – there were so many Autumn Meadowhawks on the gravel walking path that I had to choose my steps carefully to keep from stepping on them.

I walked to some bushes near the shore to see if any darners were perched there, but as soon as I stood still for a moment the meadowhawks began to gather on me.  It felt like a scene from Hitchcock’s movie, The Birds.  They were landing all over me in a frenzy.  I took some pictures showing the ones perched from my waist down, but as I took those pictures I could feel them perched on my arms, my upper body, my head, even on my face.  The pictures show over 30 on my lower body, and I would estimate there were 50 or more on my body as a whole.  I’ve had several Autumn Meadowhawks land on me before, but never anything like this.  

A gathering of Autumn Meadowhawks at Cranberry Lake in Anacortes, Washington on November 9, 2011.

The ones pictured on my lower body are only half the story – they covered me from head to toe.  It felt like a scene out of The Birds.

After taking a few pictures I looked up and saw that the air was just “full” of meadowhawks flying in all directions, hooking up in tandem or attempting to hook up.  It was similar to a mass flight of winged ants or termites.  A few darners were flying too, picking off individual meadowhawks, and also pairs in tandem, and heading for the bushes or trees to enjoy their catch.  It was quite a scene.  It’s hard to estimate the number of meadowhawks, but it must have been in the several hundreds.

I decided to go home and bring Betsy to see this phenomenon.  As I walked back to the car the meadowhawks went along for the ride on my body.  The car was a considerable distance away, and in the shade, but there were still a dozen or more dragonflies on me when I got there.  I had to “shoo” them away to keep them from getting in the car with me – though one managed to do so anyway.

When Betsy and I returned a few minutes later, the activity level was a bit lower, though still intense.  We marveled at the meadowhawks that seemed to be everywhere we looked, including all over us.  Along the shore we observed an egg-laying frenzy, with intense competition for prime sites.  As a result of the competition, many meadowhawks were being knocked into the water where they became stuck.  We ended up rescuing a dozen or more.

As we watched the egg-laying activity, the shadows of the afternoon (it was about 2:00 pm at this point) began to lengthen.  We expected to see the meadowhawks moving along the shore to stay in the sunlit areas, but at one point – quite suddenly – we noticed that the egg laying had ceased, and the air was now clear of meadowhawks.  It was almost as if someone had flipped a switch.  We’re not sure what the signal for stopping was – it wasn’t evident to us – but the meadowhawks seemed to respond en masse.

We returned the next several days, but each time the activity was completely normal again, with just a dozen or so meadowhawks along the shore.  The mass behavior seen on November 9 was a short-lived phenomenon, but one we’re happy to have experienced.

Saturday, November 11, 2017

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.

Monday, November 6, 2017

Species Spotlight: California Darner

The next "C"species for our spotlight series is the California Darner.

This is the smallest darner in our range—barely bigger than a typical skimmer. It is also the earliest darner to appear each year. Here's the Flight Season for the California Darner:

Notice that they begin to appear in March, though only about 1% of observations occur in that month. They peak in June and July, with over 60% of all observations. Finally, the last few percent of appearances occur in September.

Their range is basically west of the Rockies, with a heavy density of observations in Northern California, Oregon, and Washington.

The California Darner is a lovely dragonfly, with lots of blue along the length of the abdomen, and striking blue eyes. It has a tendency to land on the ground, or very close to it, which is a bit unusual for darners.

The key field mark for this species is as follows: no front stripes on the thorax. It's our only darner that lacks the front stripes. In addition, notice that the tenth segment of the abdomen is cream colored, and the appendages are simple in shape.

You can read much more about this dragonfly, its behavior and field marks, in my new field guide Common Dragonflies and Damselflies of the Pacific Coast, available on Amazon at the following link:

Thursday, November 2, 2017

Species Spotlight: Calico Pennant

Well, we've reached the letter C in our cavalcade of dragonfly and damselfly species.

First up is the Calico Pennant. This is a small, delicate dragonfly with wings that have beautiful colors and patterns—as is common in many pennant species. Here's a look at this striking dragonfly:

Notice the heart-shaped red spots on the abdomen, and the lovely colored patches in the wings.

We saw this dragonfly in a small field with tall grass, near a business park in Virginia. It would fly from one patch of grass to another, always very light on the wing.

Here's another look at the Calico Pennant:

We plan to visit Virginia again this coming summer. We will surely be on the lookout for more Calico Pennants!

Friday, October 27, 2017

"Open House" Field Trip

Betsy and I plan to be at Cranberry Lake from about 12:00 to 2:00 pm, weather permitting, this Saturday and Sunday. We will be looking for dragonflies and damselflies with both binoculars and a spotting scope.

Here's some of what we might be able to see:

Feel free to join us at any time during the "open house."

Saturday, October 21, 2017

Species Spotlight: Blue-ringed Dancer

We turn our attention now to a damselfly with beautifully brilliant colors—the Blue-ringed Dancer. This species is widespread in the midwest and along the east coast, but also extends into Arizona and Southern California, which is where we see it. Here's the range map, from OdonataCentral.

One of the best places to find this species, at least in Arizona, is perched on a rock in the middle of a swiftly-flowing stream, as in the photos below:

Identification is easy for this species, with the prominent blue rings along the middle sections of the abdomen. Also be sure to take a look at the thorax and head, where the rich blue colors are particularly vivid:

Notice the tendency of this species to hold the folded wings well above the abdomen when perched—a characteristic of most dancer species. In fact, you can usually tell a dancer from quite a distance just by seeing how it holds its wings. In addition, dancers tend to "flick" their wings open and shut a time or two just after landing.

One individual, seen at the Gilbert Water Ranch in Gilbert, AZ, had a weird looking face. It was kind of pink. At first it brought to mind a scene from the 1958 movie The Fly, where the hero's body has been mixed up with that of a fly during a teleporter experiment—he now has the head of a fly, and the fly has a human head. They try to find the mixed-up fly by looking in the garden for one that has a pink head. Here are some posters and photos from the movie:

Well, that was a terrifying movie for a youngster back in those days. Fortunately, the case I encountered at the Water Ranch wasn't like that at all—it was just a damselfly with a lot of pink on the head. I got closer, and finally had a better look. Here's what was going on with this individual:

Wow, one eye blue, the other pink. You don't see that everyday! Searching the bushes for a damselfly with a pink head sure made me think about the The Fly, though.

Wednesday, October 18, 2017

What Big Eyes You Have!

Dragonfly eyes are beautiful and impressive. As an example, take a look at the eyes of a young Blue Dasher, shown below.

Notice the large reddish areas on the top of the eyes. These areas are referred to as the dorsal foveae—so named because they are on the top (dorsal) surface of the eyes, and are the parts of the eyes with the sharpest vision (analogous to the vertebrate fovea). The name is ironic because the word fovea is Latin for "pit," and indeed the fovea (area of sharpest vision) of a vertebrate's eye is a pit on the surface of the retina. In the case of a dragonfly, the fovea is not a pit, but it is the area of sharpest vision.

Here's another view of dorsal foveae in dragonflies, this time on a Cardinal Meadowhawk.

One of the interesting aspects of dorsal foveae is that the ommatidia (individual eyes) in them are rather large, and point primarily in one direction. This gives the sharp vision mentioned above. It also means that when you look directly at the dorsal foveae, you see an exceptionally large pseudopupil, as shown below.

My, what big eyes you have!

This effect is perhaps best seen in Blue Dashers. Take a look for the "big eyes" next time you get a good look at a Blue Dasher. You can read more about the eyes of dragonflies in my new field guide: Common Dragonflies and Damselflies of the Pacific Coast.

Saturday, October 14, 2017

Species Spotlight: Blue-eyed Darner

The Blue-eyed Darner is one of the easiest darners to identify—even on the wing the intense blue color of their eyes, and the blue stripes on their thorax, are a dead giveaway. Here's the spread on the Blue-eyed Darner in my field guide Common Dragonflies and Damselflies of the Pacific Coast:

The flight picture above shows the blue eyes and the blue thorax stripes that jump out as this dragonfly zips by you on a warm summer afternoon.

Also, notice the photo of the female in the lower right corner of the spread. It shows a "bump," or "tubercle," under segment 1 of the abdomen. This is a distinctive feature of Rhionaeschna darners—commonly referred to as neotropic darners—though it is not always easy to see or photograph. My picture was taken at Butchart Gardens, where a female Blue-eyed Darner flew in and landed on a structure in the middle of a water fountain at just the right angle to show the bump. Mosaic (Aeshna) darners lack the tubercle.

Here's a view of another distinctive feature of Blue-eyed Darners—the forked appendages on the males.

No other male darner has forked appendages, so it's a great field mark—not that it's really needed!

The next photo shows an interesting feature that is present in all darners, but is particularly noticeable in Blue-eyed Darners. It is the small, sharp projection on the front of the thorax, just behind the eyes. This is an "egg tooth" that these darners use to break through their larval skin during emergence.

The Blue-eyed Darner is indeed a study in blue. They perch often in sunlit bushes near the shore, and are very cooperative photographic subjects.

One final feature that distinguishes neotropic from mosaic darners is shown in the next photo. Notice the light area on either side of the black "T-spot". This is found in neotropic darners, but not in mosaic darners.

So many interesting features to look for next time you're identifying darners!

Tuesday, October 10, 2017

Mount Baker Newcomers

On our recent trip to Mount Baker, Betsy and I enjoyed more than just the scenery.

We also saw some species we had never seen before at that location.

First, we saw the Hudsonian Whiteface. This is a handsome dragonfly with a black body and eyes, dark red markings on the thorax and abdomen, and a chalk-white face.

Notice also the white wing veins that extend beyond the stigmas, giving the wings a whitish tip. This field mark isn't mentioned in other field guides, but you will find it in Common Dragonflies and Damselflies of the Pacific Coast.

Another new species for this location was the Black Meadowhawk, shown below:

It's not a surprise to see this species here, because we've seen it at high altitude before—most notably at the small pond at Rainy Pass.

What a day we had a Mount Baker. We plan to return soon to enjoy the fall foliage.