Monday, September 23, 2013

Darner Mating Behavior: Attaching In Tandem

All dragonflies and damselflies mate in the so-called "wheel" or "heart-shaped" position.  In this position, the tip of the male's abdomen grabs the female behind the head in dragonflies, or on the front of her thorax in damselflies, and the tip of the female's abdomen attaches to the base of segment 2 of the male's abdomen.  A good example in the Common Green Darner is shown below:

Common Green Darners in the wheel position during mating.

The first step in attaining this position is for the male to grab the female and attach his abdomen to her, forming a tandem pair.  The following is a slow-motion video (1/4 speed) showing this attachment process in the Happy-face Darner (Paddle-tailed Darner):

A better quality video can be seen on the Dragonfly Whisperer YouTube Channel at the following link:

What's particularly interesting about this process is the way the male grips the female tightly as he makes the attachment.  Notice how the rear legs of the male slip down behind the female's forewings and pull them forward, folding them tightly against her thorax.  The male holds her like this for a moment as he shudders rapidly – apparently acquiring the desired connection – and then releases her wings and tries to take off.  In this case the female doesn't cooperate, and the male eventually gives up and departs alone.

I hadn't known before that the male folds the wings forward like that when it attaches in tandem.  It seems like quite an extreme maneuver.  You often see females with large tears in the forewings, and I wonder how often the tears are the result of this behavior.  This particular female had a large tear on the left forewing, as you can see in the photos below:

Notice the large tear just behind the nodus (bend) in the left forewing.

When the male pulls the forewings forward you can see that his leg fits nicely into that tear.  Before this video I might have considered the tear to be the result of a bird attack, but I think another possibility must be considered.

The other interesting feature of this video is the male's rapid oscillation of his abdomen (about 60 oscillations per second) just before he tries to take off.  Is he making sure he's got a good attachment?  I found one reference to something like this in Corbet, Dragonflies: Behavior and Ecology of Odonata.  On page 276 he describes a male Common Green Darner that is in tandem when it's attacked by another male.  According to Corbet, "the tandem male shakes its abdomen in a convulsive movement detectable to the human observer only when portrayed in slow motion."  I wonder if this is the same basic behavior.

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