Splash-Dunk/Spin-Dry Analysis for 2011 to 2018

The splash-dunk/spin-dry behavior is an interesting, and previously unreported, aspect of dragonfly behavior. Here's an illustration of the basic features of the behavior:



A dragonfly—often a male Paddle-tailed Darner—plows headfirst into the water (the splash-dunk) a number of times to bathe. When satisfied that it is sufficiently clean, it gains altitude and spins head-over-heels at 1,000 rpm to dry off. This is the spin-dry. The dragonfly spins about a horizontal axis during the spin-dry, like a bicycle wheel, as indicated in the following illustration:

We first started taking data on this behavior in 2011, and since that time we've observed 762 separate splash-dunks events. For each event, we record the number of splash-dunks, which ranges from 1 to 8. The distribution of splash-dunk numbers in an event is shown below:



Notice that roughly 40% of the events consist of a single splash-dunk, many have 2 or 3 splash-dunks, and a couple events have had 8 splash-dunks. The average number of splash-dunks per event is 2.32, which is unchanged to three significant figures over the last three years.

The temporal distribution of splash-dunks has also been stable over the last few years. Here are the results for the number of splash-dunk events seen per month from 2011 to 2018:



The peak of the season is September, which also—not coincidentally—is the peak of the flight season for the Paddle-tailed Darner.

We also keep track of the number of spin-drys seen at the end of an event. Here are the results:



In almost 30% of the events, a spin-dry isn't seen, either because the dragonfly didn't do a spin-dry, or—more likely—because it did a spin-dry out of view. A single spin-dry is seen in about 65% of the events. Sometimes a dragonfly does a spin-dry, and then immediately does another. This is seen in roughly 5% of the events. In addition, a couple events results in 3 spin-drys.

With so many events observed over the last 8 years, the results have become very stable and reproducible from year to year.

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.

The Dot-tailed Whiteface Does A Body Slam

On a recent trip to Heart Lake here in Anacortes, I observed a new behavior exhibited by the Dot-tailed Whiteface. Here's a picture of an individual of this species from Heart Lake:



Notice the chalk-white face, black eyes, clear wings, and black body with a yellow dot near the tip of the abdomen. This is surely one of the easiest IDs to make in dragonflying.

Getting back to the behavior, I was taking a video of general dragonfly activity at the lake. When I got home and viewed the video on the computer I noticed some unusual movement in the lower right corner. On closer inspection, I saw that a bluet was harassing a Dot-tailed Whiteface, eventually grabbing its abdomen. The whiteface immediately did a spin move—similar to what dragonflies do in a spin-dry, only in this case it was "shedding" the damselfly rather than water.

Here's a video clip showing the body slam. It's grainy because it's an enlargement of the lower right corner of the full video:

You can see the full video at the following link:

https://www.youtube.com/watch?v=QuY34erRHpY

Fascinating behavior, where the dragonfly adapts one behavior—spin-dry to shed water—to another ver different situation—spin-dry to shed a damselfly.

Find out more about the splash-dunk/spin-dry behavior, as well as about the Dot-tailed Whiteface, in my new field guide, Common dragonflies and Damselflies of the Pacific Coast. You can find the book at the following link:

https://www.amazon.com/gp/product/1934199265/ref=s9u_simh_gw_i1?ie=UTF8&fpl=fresh&pd_rd_i=1934199265&pd_rd_r=4Q8FNWQMZKPZ7GYWQB31&pd_rd_w=c79uB&pd_rd_wg=lb3xg&pf_rd_m=ATVPDKIKX0DER&pf_rd_s=&pf_rd_r=038QHD1N13Z2D7NWAP1Q&pf_rd_t=36701&pf_rd_p=1cf9d009-399c-49e1-901a-7b8786e59436&pf_rd_i=desktop

You never know when a trip to the field will result in new behavior.