Wednesday, January 17, 2018

Species Spotlight: Cardinal Meadowhawk

In these deep winter months, when the dragonflying days of summer seem so far away, it's nice to look at one of the highlights of the dragonfly season—the Cardinal Meadowhawk.

This is primarily a western species, as can be seen in their range map:

Cardinal Meadowhawks are so intensely red that they almost seem unreal—as if they might be made of bright red plastic. Their abdomens are pure red, with no consistent black markings as in so many meadowhawks. In addition, the abdomen is noticeably flattened; that is, wider than it is high. Their eyes and face are red, and they have two white spots on the sides of the thorax. In fact, these white spots are what remain of white stripes in younger individuals. With age the stripes fade away, leaving just a spot at the base of each stripe. The white spots are often hard to see because the Cardinal Meadowhawk has a tendency to fold its wings forward when perched, hiding the sides of the thorax.

Better field marks, and ones that aren't mentioned in many field guides, are the dark red patches at the base of the wings—especially the hindwings. These patches are diagnostic for this species, and are readily seen even when the dragonfly is perched, facing away from you, and folding its wings forward.

Here's another look at the dark red (tending toward black with age) patches in the wings:

Find out more about this species, and the other common dragonfly and damselfly species of the Pacific Coast, in my new field guide:

Thursday, January 4, 2018

Species Spotlight: Canada Darner

The next species to grace the spotlight, the Canada Darner, is one that is not seen all that often—and when it is spotted, it's often high up on a tree trunk. Another one of the mosaic darners, a group that that includes the Happy-face Darner (Paddle-tailed Darner), the Canada Darner is best known by its "notched" side stripes that look like slippers or clogs.

Here's a typical view of a Canada Darner, perched on the vertical surface of a light-colored tree trunk.

A closer look reveals simple appendages and cream-colored spots on the last segment 10 of the abdomen.

These features are consistent with both a Canada Darner and a Variable Darner, but the prominent front stripes on the thorax, and the robust stripe on the top of segment 2, indicate that the Canada Darner is the more likely identification. To be certain, though, we need to see the side stripes of the thorax.

The next photo shows another Canada Darner perched high in a tree. In this case, you can just barely see the notched shape of the side stripe through the front wing. This confirms the identification.

Here's a better look at the side stripes. Notice that the forward side stripe looks like a house slipper, or a clog, with the toes near the dragonfly's head. The rear side stripe is shaped like a short spike pointing forward.

A slightly closer view of the same individual:

We haven't seen this species in Anacortes, but it is seen occasionally at Barnaby Slough, high in the foothills of the Cascades. We see it on a more regular basis at the Beaver Pond near Sun Mountain Lodge in eastern Washington.

Find out more about this species, and the other mosaic darners, in my new field guide:

Monday, January 1, 2018

Happy New Year!

Well, it's here—2018. Here's wishing you and yours a happy and fulfilling New Year.

And may it be a happy New Year as well!

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.