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.
Black Saddlebags (T. lacerata) laying eggs and reattching.
No comments:
Post a Comment