Saturday, September 29, 2012

1.5 Damselflies – Darner Predation In Action

Strange things happen in nature – things you might never predict in advance.  No one predicted superconductivity, for example, even though it's a direct consequence of well-known physics.

Here's an example from biology.  Once in a while you look in the bushes and see something like the following:

1.5 dameslflies – a female Tule Bluet plus the abdomen of her former mate.

What's going on here?  At first it looks like some sort of strange creature with a weird body plan, but then you realize it's a female damselfly with the abdomen of a male attached behind her head.  That's strange alright, not something you might have predicted in advance, but then you ask yourself, "How did that come about?"

The first thought is generally that it's the result of a pair of damselflies in tandem being attacked by a bird that makes off with part of the male.  That's certainly reasonable, and probably happens a lot, though it does beg the question of why the bird doesn't finish off the job since the female with the attached abdomen is an easy catch.

The explanation is quite different in this case, however.  I was observing a male California Darner on the shore of Cranberry Lake – California Darners like to perch on the ground, as compared with Paddle-tailed Darners, Blue-eyed Darners, and Shadow Darners that prefer to perch in bushes about chest high.  In any case, the darner took off and I watched as it flew over the water.  In a second it attacked a pair of Tule Bluets that were flying in tandem.  The darner had quite a struggle on its hands, and it flew toward some bushes on the shore.  I followed, expecting it to land and process its catch.  Instead, something fell from the darner into the bushes, and it continued flying.  When I looked in the bush I saw the 1.5 damselfly pictured above.  The darner had snipped off the male at the base of its abdomen, and continued in flight to eat the nice, meaty thorax.

Since that time we've observed similar types of darner attacks a number of times.  One of the most common happens near the end of the season, when Paddle-tailed Darners and Autumn Meadowhawks are particularly numerous.  We've seen several instances of a darner grabbing a pair of Autumn Meadowhawks in tandem.  The darner sometimes snips off the abdomen of the male meadowhawk, eats the thorax, and leaves the female with an abdomen attached.  Sometimes the darner eats the entire male while it is still attached to the female.  When it gets most of the way through the abdomen the female is released, and she rests in the vegetation before flying off as the darner finishes its meal.

Yes, strange things happen in nature.

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