Taking Flight (Well-Nigh Wordless Wednesday)

Last week was National Moth Week, so I have once again been taking countless photos of moths both at my annual moth night at work and in my own backyard.  Many of my photos turn out well enough to help me get an ID for the things I see, but every now and again I get one like this:

Photo of a moth flying away from the camera

Almost…

SOOOOO frustrating!

(I’ve been away at a conference and busy as heck at work recently, but I should get back to my normal schedule here for a while.  See you Friday!)

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Unless otherwise stated, all text, images, and video are copyright © C. L. Goforth
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Aerial Plankton

aerial plankton

Aerial plankton. Image taken from npr.org.

Okay okay.  I know I promised a post about a dragonfly swarming paper this time, but I decided I should talk about a related subject first: aerial plankton. Don’t worry – I’ll get to the dragonfly paper next time!   I am nearly wholly engrossed by the dragonfly swarming information that’s been coming my way and I will definitely go right back to it.  But this topic is likely an important component of the migratory swarms seen in dragonflies and I thought I should discuss it before I do the dragonfly paper.

If you’re like most people, you probably don’t know what aerial plankton is and may never have considered the possibility that it exists.  But most people know at least something about the plankton that live in oceans, marine plankton.  If you do, the concept is very similar.  The definition on Wikipedia for plankton is pretty good: Plankton are any drifting organisms (animals, plants, archaea, or bacteria) that inhabit the pelagic zone of oceans, seas, or bodies of fresh water.  Most of what we think of as plankton are little crustaceans such as krill or amphipods.  These are the things that are eaten by whales using baleen and several other large marine mammals.  Though small, they’re very important in marine habitats, both as a food source and for the many other services they provide.

Aerial plankton is similar in that it is made up of small creatures drifting along on currents.  However, instead of drifting in water currents, they drift through the air!  There are many, many species of insects, spiders, and other small organisms that make up the aerial plankton community and these creatures rely on wind currents to carry them from one place to another.  Basically, any small animal that can catch and updraft or find another way to get high enough into the air to get caught up by an air current becomes part of the aerial plankton.  Different things will use different methods to launch themselves into the currents.  Most insects fly.  Many spiders are known to “balloon.”  They extend strands of silk into the air that are caught in the wind, carrying the spider up into the atmosphere and away on the wind currents.  Ever read Charlotte’s Web?  The spiders leaving the egg sack at the end of the story were doing this exact thing.  Charlotte’s children became part of the aerial plankton!

It just so happens that this topic is one I’ve been just itching to cover recently thanks to a story by Robert Krulwich that popped up on NPR a few weeks ago.  Robert Krulwich does amazing reports on scientific topics and the animations that frequently accompany his stories are truly brilliant. They’re simple to understand, fun to watch, and get the main points across in a wholly engaging manner. I highly recommend that you check out his work if you haven’t already!  Rather than telling you why animals might want to drift around on air currents and how many organisms are floating around on our heads at any given moment, I’m going to direct you to Robert Krulwich’s story on NPR.  You can read the full article using the link, or you can just watch the animation, which sums it all up in a very succinct way:

I think this little video is quite brilliant.  So there are billions of animals floating through the air at any given time!  And they’re trying to move from one place to another efficiently.  There are certainly downsides to this sort of travel, the most important of which is this: these animals are really at the mercy of the winds and have very little control over where they end up.  It’s rather like hot air ballooning in that way.  As May Berenbaum said in the video, sometimes an animal ends up in a worse spot than when they started out.  It happens.  It probably happens a lot!  But many of those animals also make it to a better place than they started and make a good life for themselves in a new area.

Wandering glider (Pantala flavescens)

Wandering glider (Pantala flavescens)

So why am I bringing up aerial plankton?  Well, dragonflies likely use these same wind currents when they migrate.  They are, technically, becoming part of the aerial plankton when they do.  Some dragonflies are superb fliers, such as the wandering glider pictured at the right.  This dragonfly is known to fly over oceans and is found on all continents naturally.  While it can fly for many, many hours without resting, even these insects are probably getting a boost from the wind as they fly across oceans in search of new homes.  By using the power of the wind to propel them along, they can let the wind do some of the work for them and rest their wings to some extent.

But there’s another reason that aerial plankton and dragonflies are related as well.  Aerial plankton is a very valuable source of food for many animals, including predatory and scavenging insects.  What comes up, must come down, and aerial plankton is no exception.  Eventually, all of those billions of animals fall out of the sky.  Sometimes those things come down alive and other times they come down dead, but they’re important as a food source either way.  Storms are particularly hard on the aerial plankton community.  They can knock vast numbers of animals out of the sky and push them toward the ground, making them easy targets for things that might want to eat them when they do.  Dragonflies are thought to take advantage of this occasional shower of food from the sky and feast after storms.  This behavior is likely related to some of the behaviors observed in the big migratory swarms that I’ll be talking about next time, which is why I wanted to discuss aerial plankton first.

Aerial plankton is a vital dietary component for several insect species, but two come instantly to mind.  There is one insect order that is absolutely coveted by entomologists for collections because they are so hard to find and so rare to collect: the Grylloblattidae.  These insects live on snow fields in the Arctic and on the tops of very high and very cold mountains that are typically covered in snow.  Very few invertebrates can survive in these conditions (indeed, few animals live in them period!), so the grylloblattids rely almost entirely on aerial plankton as food.  Things fall out of the sky, land on the snow or ice, and the grylloblattids go skitting around on the snow collecting them.  These insects likely couldn’t survive at all without aerial plankton.   One of the only truly marine insects also depends on aerial plankton as a food source.  The water striders belonging to the genus Halobtes live on the open ocean, on top of the water like their freshwater relatives.  They’ll eat things from the water, but they also eat things that fall on the ocean’s surface from the sky and become trapped.  Aerial plankton likely forms a large part of the Halobates diet.

The next two posts will focus on dragonfly swarms.  First up is the discussion of the migratory swarm paper.  Then, I’m going to give another update on swarming activity in the US, including a map I’m developing of all of the sightings I’m collecting.  And as always, if you happen to see a dragonfly swarm, I’d love to hear about it!  Head over to my Contact page to submit a report.  I’m averaging about 10 reports a day this month so far, so keep them coming!

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Unless otherwise stated, all text, images, and video are copyright © 2010 DragonflyWoman.wordpress.com

A Trip to Sweetwater Wetlands

Before I get back to the water bugs, I want to continue my detour for a few posts and talk about some dragonflies I saw yesterday.  I needed to take some dragonfly photos, so my fiancee and I went to a constructed wetland in Tucson called Sweetwater to shoot.  Sweetwater is part of one of the wastewater treatment plants in Tucson and is fed entirely with reclaimed water and secondarily treated wastewater.  It can smell pretty bad at times (it IS made up of treated wastewater after all), but if you can overlook the scent it’s gorgeous and wholly worth a visit.  All those nutrients in the water do wonders for the plant life that grows in the water:

Sweetwater Wetland

Sweetwater Wetland

As you can see, the nutrient-rich water of the wetland is able to support a wide variety of aquatic plants.  Yesterday, the wetlands were full of cattails (the dark green bushy looking things on the right side of the picture), rushes, sedges, and duckweed.  Most of the bright green stuff floating on the water in this picture is duckweed, NOT algae, though there was definitely algae there as well.  The wetland also suports a variety of trees and shrubs and many different species of wildlife.  All those dark spots in the picture are ducks.  I’ve also seen several snakes and lizards, many other birds, and even a bobcat once!  And then there are, of course, the dragonflies.  Thousands of them.  I think Sweetwater is the best place in Tucson to see dragonflies.

We saw several dragonfly species, including green darners (Anax junius), arroyo darners (Aeshna dugesi), blue-eyed darners (Rhionaeshna multicolor),  flame skimmers (Libellula saturata), roseate skimmers (Orthemis ferruginea), blue dashers (Pachydiplax longipennis), Mexican amberwings (Perithemis intensa), variegated meadowhawks (Sympetrum corruptum), and black saddlebags (Tramea lacerata).  We also saw one species of damselfly (though we weren’t really looking hard for the damselflies either – there may have been more), the desert firetail (Telebasis salva).  Most of the dragonflies were flying above the cattails or were resting on them in various positions.  Some were even in the obelisk position, which I have talked about before in another post on dragonflies.

I got some good shots of several different species, which I’ll go over in my next post.  However, I was most thrilled with all of the large flying dragonflies, the darners.  I like taking pictures of flying dragonflies the best because they are the hardest to shoot.  This is the same reason I got interested in dragonflies in the first place – catching dragonflies for my collections for 4-H was the biggest challenge.  I have yet to get a really, really good shot of a flying dragonfly, but I keep at it, and I got some pretty decent shots today.

This is Anax junius, the green darner:

Anax junius mating pair

Anax junius mating pair

This is a mating pair.  The male, the more brightly colored one with the blue abdomen, had just grabbed his mate in preparation for mating, and then they promptly fell out of the tree onto the sidewalk, right next to me!  They sat there in this position for almost a minute while I snapped away with my camera.  Then they flew off to mate and lay eggs.  Anax junius was very abundant at Sweetwater yesterday, so I ended up getting a lot of pictures of them.  They are fliers, so they don’t land very often.  That also makes them fairly hard to photograph – they don’t sit still for very long.  So, most of the photos I got were of these insects flying, and most of them looked like this:

Dragonfly photo

Typical dragonfly flight photo

The little smudge in the photo at the tip of the big blue arrow is the dragonfly!   I took about 90 photos of Anax in flight, and these were the best:

green darner in flight

green darner in flight

green darner in flight

green darner in flight

green darner in flight

green darner in flight

What I particularly liked about these images, aside from the fact that they are actually mostly in focus, is that you can see the legs of the dragonflies folded up underneath their thoraxes.  Having the legs folded up under the body likely helps the dragonflies fly more efficiently.  If they let their legs dangle down underneath them, they are likely to slow the dragonflies down, get snagged on the vegetation when they fly low, and otherwise cause problems.  So, they fly with them tightly folded under their bodies and only stretch them out when they grab food in midair.  It’s fun to be able to see that they do this, but it would be hard to see by observing them directly because they fly so fast and so erratically.  It’s easy to see in the photos.

Like in my post on the species from the dragonfly swarm, you can clearly see from these photos that dragonflies are able to move all four of their wings independently from one another.  For example, in the top photo, you can see that the forewings are both moving down while the hindwings are moving up.  This ability to move their wings independently contributes significantly to the amazing agility that dragonflies exhibit.  If you’ve ever seen dragonflies flying, you know how fast and agile they are.  They can stop in midair, make 180 degree turns, fly backwards, hover, and do all sorts of other things that are nigh impossible for most flying animals.  They dart all over the place, which is why it’s hard to get photos of them in flight.  If you’re dealing with a flier species, such as Anax junius, they are going to be moving constantly too.  Another reason it’s hard to get good photos of dragonflies in flight is the behavior you see in this photo:

green darners in flight

green darners in flight

Dragonflies are highly territorial and protect their territories from other dragonflies that might be trying to steal their access to prime egg laying habitat or other valuable resources.  In flier species, the males typically patrol, or fly within the boundaries of their territories, looking out for females to mate with, food, and males who might want to try to claim the territory for themselves.  In this photo, the dragonfly at the top tried to steal the territory that belonged to the dragonfly on the bottom.  The owner of the territory, the dragonfly on the bottom, successfully chased the would-be thief out away from his territory.  In the photo, the territory holder is returning to his territory to continue patrolling while the loser is flying away to find another spot, hopefully one guarded by a wimpy male.  Because there are usually fewer territories available than dragonflies at a pond, these battles are constantly occurring.  When a male sees another male that might enter his territory, he will immediately change directions and charge the tresspasser in an attempt to protect his territory.  This means that the dragonflies are darting back and forth constantly.  You might track one dragonfly and just be ready to snap a photo when he stops, turns around, and zips off in a completely diferent direction.  It’s very hard to predict where a dragonfly is going to be at any given time, so it is difficult to get good photos of them in flight.

Next time I’ll go over how to identify some of the species that we saw at Sweetwater, then it’s back to the giant water bugs for a while!

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Text and images copyright © 2009 DragonflyWoman.wordpress.com

Photos from the swarm

I went out to Lakeside Lake with a friend early this morning to take some photos of the dragonfly swarm that’s been forming there.  (See my previous post for more information about the swarm and a video of the behavior.)  The swarm’s been forming every morning this week!  The dragonflies were flying constantly and darting here and there very unpredictably, so it was nearly impossible to get a good shot, but I got a few I thought were worthy of showing here.  My apologies for the general blurriness – these things are FAST!

Pantala hymenaea

Spot wing glider (Pantala hymenaea)

Pantala hymenaea banking

Spot-winged Glider (Pantala hymenaea) banking during a turn

Pantala flavescens

Wandering glider (Pantala flavescens)

A few things I noticed about the dragonflies in the photos I took:

1) The forewings of the dragonflies move separately from the hindwings.  I already knew this, but it’s hard to see it when they’re flying around because their wings move so fast.  It’s very obvious in the photos though!

2) When the dragonflies turned sharply in flight, they usually kept their heads parallel to the ground.  Even though their bodies were twisting and turning as they glided about, their heads remained in about the same position the whole time. This resulted in some pretty gnarly looking photos where the dragonflies’ heads looked like they were on upside down!  I unfortunately didn’t not get a clear shot of this to show you…

3) Dragonflies can definitely fly backwards.  Dragonflies are among the most agile of flighted animals and part of what makes them so agile is their ability to fly backwards, a very difficult maneuver.  It was frustrating to get a shot all lined up only to have the dragonfly zoom BACKWARDS out of the photo at the last second!

4) Dragonflies at rest are a LOT easier to photograph than flying ones!  Case in point: the photo I posted last week (see myDragonfly Sighting post) was of a dragonfly sitting on a bush branch.  I took 3 photos of the dragonfly before it took off and I considered all 3 good enough to post.  Today I took 377 photos.  About a third of them didn’t end up having any dragonflies in them at all.  Of the 236 that actually contained dragonflies, the vast majority showed the dragonflies as blurry, indistinct blobs of color.  I only got 13 shots I thought were decent at all, and my best one, the wandering glider above, is still far from perfect.  I like the photo more for the contrasting colors than anything else.

Regardless of the difficulty of the photography, it was still really fun!  If nothing else, it was amusing to TRY to get some good photos of these guys.  (I can’t help it – I’m drawn to the difficult photographic subjects, if only so I can practice and improve my skills.)  Even if we hadn’t gotten any good shots, it still would have been worth the trip to the lake just to see so many dragonflies in one place at one time.  This swarm is pretty darned impressive and watching hundreds of dragonflies lazily flying around a hill in the morning sun is a fabulous way to spend a weekend morning.

Be sure to check out the photo my friend posted from this morning’s shooting.  The photo she posted is better than any of mine, so I hope you’ll take a look!

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Have you seen a dragonfly swarm?

I am tracking swarms so I can learn more about this interesting behavior.  If you see one, I’d love to hear from you!  Please visit my Report a Dragonfly Swarm page to fill out the official report form.

    I welcome any information that you’re willing to provide about your swarm!  The more details you’re willing to provide, the more helpful your report will be, but I’ll happily take anything you’re willing to share.  Reports so far have varied from a few words to novellas, and it’s all useful.

    Thanks!

    (Added June 30, 2010)

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    Text and images copyright © 2009-2010 DragonflyWoman.wordpress.com