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.

Thursday, September 27, 2012

Autumn Has Arrived!

One of my favorite examples of dragonfly haiku is the following:

Red dragonfly on my shoulder,
calls me his friend.
Autumn has arrived.

The sentiment of this haiku was played out in real life today at Cranberry Lake, where Autumn Meadowhawks (red dragonflies) are showing up in numbers and perching on shoulders, hats, and any other available surface.

In our area, if you see a red dragonfly this time of year you've already identified it – it's an Autumn Meadowhawk.

Here are a few pictures from Cranberry Lake showing the subject of the haiku:

Red dragonfly on Betsy's shoulder – and hat.  Autumn Meadowhawks really are the friendliest dragonfly.

Autumn Meadowhawks enjoy basking in whatever sunlight is available.

Autumn Meadowhawks in the wheel position.

Wednesday, September 26, 2012

Black Meadowhawks At Barnaby Slough: Another County Record, This Time In Skagit County

It's been an unusual year for dragonflies – at least in our area.  The activity level has been low overall, and what we're seeing is often quite out of the ordinary.

For example, the activity at Cranberry Lake has been so low that I haven't given a late-season field trip there as I would have liked. Even so, we saw many American Emeralds at Cranberry Lake earlier this year, compared to just one seen there over the previous five years.  We went from almost nothing to a population just like that.

Next, I went to Thunder Lake in July and saw an incredible number of Chalk-fronted Corporals.  Before that, Betsy and I had seen a single individual at Barnaby Slough, which was a record for Skagit County.  Again, we went from almost nothing to a roaring population.

Then, about a week ago, we went to Lake Terrell in Whatcom county and found Black Meadowhawks in an area where we had never seen them before.  That was a record for Whatcom County, as detailed previously here:

A few days ago we went to Barnaby Slough.  We're checking things out, seeing the usual suspects, and then all of a sudden I spot a small, dark dragonfly landing on the walking path.  I check it with my binoculars and it's a Black Meadowhawk!  I can hardly believe it.  This time it's a county record for Skagit County.  Several more males were seen to flush from the trail and fly to a sunken pond nearby.  We haven't been looking for county records, but for some reason they've been coming to us.  As I said, this has been an unusual year for dragonflies in our area.

Here are some photos of a Black Meadowhawk at Barnaby Slough:

A male Black Meadowhawk putting on a pose for me at Barnaby Slough.

This is a relatively young individual.  It will darken with age.

Notice the bi-colored eye and the face that is dark in front and light-colored on the sides.

Monday, September 24, 2012

Happy-face Haiku

The Happy-face Dragonfly (Paddle-tailed Darner) is very common this time of year – often the most common dragonfly at a given location.  That's certainly the case at Cranberry Lake, where we saw a nice male looking up at us from the bushes.  He inspired the following haiku in his honor:

Perched in the bushes,
smiling up at me,
the Happy-face Dragonfly.

Mr. Happy-face, with his infectious smile.

Notice that his wings are a bit grubby, with foreign material adhering to them.  Perhaps he's thinking about doing some splash-dunks!

Friday, September 21, 2012

Black Meadowhawks At Lake Terrell: A County Record For Whatcom County

Betsy and I visited Lake Terrell near Ferndale, WA a few days ago.  It's one of our favorite dragonflying sites, and we go there every year.

This year the activity level was really quite low, but there was a surprise for us.  As we walked along one of the grassy paths back from the shore we suddenly spotted a very small, dark, delicate dragonfly.  It was a male Black Meadowhawk.  A few minutes later we saw a female as well.  We've only seen Black Meadowhawks at Rainy Pass and near Winthrop – never in our usual areas near Puget Sound.  Though we weren't looking for one, it turns out that a Black Meadowhawk in Whatcom County is indeed a county record.

Here are photos of the Black Meadowhawks at Lake Terrell:

A male Black Meadowhawk perched on the ground.

The same male at a different location on the walking path.  These dragonflies are so small and dark that they are hard to keep track of when they take wing.

A female Black Meadowhawk in the same area where the male was observed.

Wednesday, September 19, 2012

River Jewelwings

A few weeks ago Betsy and I drove to a location just south of Olympia to look for a striking damselfly known as the River Jewelwing.  We've only seen this odonate twice before, both times a single male at Stossel Creek near Duvall, WA.  According to reports, the River Jewelwing can be seen in numbers where State Route 12 crosses the Black River, so we headed south to check it out.  We had stopped at the same location on our way home from Arizona in May, but that was too early in the season and none were seen.  This trip was during the peak of the season, and several – both males and females – were seen flitting along the shore of the river.

The Black River is beautiful at the location populated by the jewelwings.  Here are a couple shots that show the setting.

Betsy on the shore of the Black River.

The Black River.  Notice the submergent vegetation just below the surface of the river.

Just visiting this location is pleasant enough, but if you look closely in the vegetation along the shore you'll see some flashes of iridescent blue and green.  You'll also see wings flapping with prominent black patches.  These are the River Jewelwings going about their daily activity.

Here are a couple shots of the male River Jewelwing.

A male River Jewelwing with its wings slightly parted.

Side view of a male River Jewelwing on the shore of the Black River.

The beautiful colors of this damselfly are due to iridescence, which is a very different mechanism from colors produced by pigments.  Here's a comparison between the two mechanisms:

Pigment Colors  Pigments absorb certain colors and reflect others, resulting in a specific color when viewed in white light.  The observed color is the same regardless of the viewing angle, since it depends only on which colors are reflected.

Iridescent Colors  Iridescent materials produce colors by interference.  What this means is that all colors of light are reflected, but some colors cancel themselves out due to phase shifts caused by the structure of the material.

One of the key characteristics that distinguish pigment colors from iridescent colors is that iridescent colors change with the viewing angle, because changing the viewing angle changes the phase shift.  This effect can be seen in cases like the head and neck of a male Mallard, which can appear either blue or green.  The same effect is seen in the River Jewelwing, as we can see below:

A male River Jewelwing viewed from one side.  The body is dark blue.

The same individual as above, this time viewed from the other side.  Its body is now brilliant green.

Notice that even the leading edge of the wings (the costa) changes color from blue to green along with the thorax and abdomen.

The males were constantly patrolling along the shore, defending their territories.  Here are a couple males flashing their wings as one tries to displace the other.

Male River Jewelwings competing for space along the shore.

Female River Jewelwings were present as well – our first opportunity to view them.  They share the iridescent body colors of the male, and also have white spots (the stigmas) at the tip of their wings.

A female River Jewelwing.  Notice the iridescent body and the white spots on the wings.

Many female River Jewelwings were seen in the male's territories, but no mating activity was observed.

All in all, it was a beautiful day at a wonderful location full of special damselflies.