Why Dragonflies Are the Best Insects (The Dragonfly Trilogy, Part One)

Hello everyone!  I took a week off for Christmas, but I’m now back at my computer and looking forward to blogging during the new year.  Hope you all enjoyed your holidays!

For the next few posts, I’m going to talk about odonates.  Dragonflies have been my favorite insects for ages and I find them completely fascinating.  They are also special insects – they do things no other insects do and they have body structures that no other insects have.  So, for this post, I’m going to talk about these special traits, the reasons why I think dragonflies are the most amazing insects in the world.  Next time, I’m going to talk about dragonfly territorial behaviors, and then I’ll finish up my dragonfly trilogy with a From the Literature entry that relates to dragonfly territoriality.  I hope you enjoy The Dragonfly Trilogy!

Last summer, I wrote about the difference between dragonfly and damselfly nymphs.  If you haven’t read that post and/or don’t know how to tell dragonfly and damselfly nymphs apart, I recommend that you do so before reading further.  If you have read the post or know a bit about dragonflies already, you know that one of the very special things that dragonflies nymphs have is their fantastic mouthpart (see photo).

Dragonfly mouthparts side view

Dragonfly mouthparts, side view

This bizarre mouthpart is definitely one of the most amazing things about odonates – and they are the only insects in the world that have them.  I personally think it gives the odonates a sort of alien-like appearance.  Can’t you just see this sort of structure popping up in an alien invasion movie?!  More practically, this mouthpart allows the odonates to be fierce predators and places them firmly near the top of most aquatic food chains.

All odonate nymphs have this mouthpart, but the dragonflies have another unique structure that makes them even more bizarre and interesting: rectal gills.  Recall that dragonflies and damselflies have different appendages on the ends of their bodies.  The damselflies have three leaf-like gills attached at the tips of their abdomens (see photo).

Damselfly gills

Damselfly gills

Though the dragonflies don’t have these structures, they still have gills.  Rather than keeping them exposed to the water like the damselflies do, however, they keep their gills inside their bodies!  Dragonflies have a chamber inside their abdomens called the rectal chamber that is lined with gills.  Due to the physics of respiration in water and because the gills are inside the body, dragonfly nymphs have to pump water in and out of the rectal chamber to allow the gills to absorb oxygen from the water.  (If you ever have a chance to see a dragonfly nymph, you’ll likely see the abdomen pulsing – it is pumping water through its rectal chamber.)  The opening to the rectal chamber is at the back end of the bugs, so the dragonfly nymphs are effectively breathing through their butts!  If that doesn’t make dragonflies one of the coolest animals in the world, I don’t know what does.

The rectal chamber also allows the dragonfly nymphs to do a great behavior: jet propulsion.  Due to some properties of physics, they can forcefully squeeze the water out of their gill chamber to propel themselves forward very rapidly.  If you’ve ever seen a fan boat (they’re usually used in swamps) on TV or in person, it works about the same way.  By pumping water into the rectal chamber and shooting it back out at a high speed, a dragonfly can move very fast and entirely without the use of its legs!  To see this behavior in action, take a look at this video, paying special attention to their legs:

Did you see the little dimples in the surface of the water behind the dragonfly?  That is the water jet being expelled from the rectal chamber and hitting the surface of the water.  The jet propulsion behavior helps the dragonfly nymphs avoid being eaten by predators by allowing them to escape very quickly when they are startled.  And, it is one more reason why dragonflies are amazing insects.

So dragonfly nymphs have the alien-looking extendable mouthpart, internal gills that make them breathe through their butts, and jet propulsion.  What about the adults?  The adults are just as bizarre!

green darner in flight

Anax junius in flight

First, let’s consider the wings.  Dragonflies are among the strongest and most agile fliers of the insects.  They are able to do this because of another strange bodily structure.  In almost all insects, the wing muscles don’t attach directly to the base of the wings.  Instead, they usually attach to the inner walls of the thorax so that when the insect contracts the wing muscles, the whole thorax deforms.  This indirectly makes the wings move.  These sort of flight muscles are called indirect flight muscles because the wing muscles do not attach directly to the wings.  Dragonflies, however, have direct flight muscles.  Moreover, each wing has its own muscle.  This means that dragonflies can move all four wings independently of each other.  It is this trait that gives them their awesome flight capabilities, such as their ability to come to a dead stop while making a 180 degree turn and their ability to fly backwards.  Dragonflies are such great fliers because they have different wing muscles than most other insects.  This is also what allows them to grab a flying insect (or the occasional hummingbird!) in flight so that they can eat it.

Adult dragonflies have one other unique body structure that makes them fabulous.  The males and females both have their genitalia at the ends of their bodies, the tips of their abdomens.  However, due the way dragonflies mate, dragonfly males can’t use these structures to transfer sperm to the females.  A dragonfly male grasps the female behind the head as they mate, which means that his genitalia are far from the female’s.  So, dragonfly males have a second set of genitalia on the abdomen near the thorax!  Before he mates with a female, a male will transfer sperm from the genitalia at the end of his abdomen (the primary genitalia) to the genitalia at the base of his abdomen (the secondary genitalia):

male dragonfly genitalia

Male dragonfly genitalia (Pantala hymenaea)

Once a male dragonfly grasps the female with his abdomen, he curls her body around so that her genitalia come into contact with his secondary genitalia, thus transferring sperm from his body to her’s:

mating dragonflies

Dragonflies mating (Pachydiplax longipennis). The male is the blue dragonfly on top and the female is the brown dragonfly on the bottom.

Some dragonflies fly around while they mate and others will find somewhere to land, but you’ll see this formation in virtually all mating dragonflies.  Pretty neat, eh?  I’ll talk more about dragonfly mating next time when I discuss dragonfly territorial behaviors.

Because dragonflies have this complicated mating system (which is amazing even if there wasn’t anything else going on), they also have two sets of genitalia, one of many reasons why I think dragonflies are the best insects.  This also makes it very easy to tell male and female dragonflies apart.  If you have a dragonfly in your net or your hand or a really good photo, look for a bump on the underside of the abdomen near its joint with the thorax.  If there’s a bump there, it’s a male.  If the underside of the dragonfly is smooth, it’s a female.  It’s easy!

So, did I convince you that dragonflies are the best insects?  If not, I hope you at least have a greater appreciation for the things that make dragonflies unique and fascinating.  Between their anatomical oddities and their amazing behaviors, dragonflies are some of the most interesting animals to study and one of the most widely appreciated insects.  If you have an opportunity, I highly encourage you to watch any dragonflies near your home.  You are sure to discover many new and interesting things about dragonflies that you can add to the list of things that make dragonflies so cool.  And who knows?  You might even find yourself agreeing with me!

Tune in next time for part two of the Dragonfly Trilogy: Territorial Behaviors in Dragonflies.

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Text, images, and video copyright © 2009 DragonflyWoman.wordpress.com

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Invertebrates Using Tools! Octopus Coconut Carrying Behavior

Okay, I know this has nothing to do with insects, but octopusses ARE aquatic and they ARE invertebrates (not to mention they are completely fabulous), so I just had to share this news story briefly before I post my next insect entry.  I’ve always had a soft spot in my heart for octopusses and this discovery reminds me of just how amazing these animals really are.

octopus in coconut

Veined octopus hiding in coconut halves. Photo from nationalgeographic.com.

Scientists have discovered many wonderful behaviors in octopusses, but a team of marine biologists, led by Australian researcher Julian Finn, recently came across a species of octopus that does an amazing thing: it uses tools!  In a paper published today in the journal Current Biology, the researchers reported their observations of the veined octopus (Amphioctopus marginatus) of Indonesia.   This species digs up halved coconut shells from the seafloor, then carries them around by suctioning them to the bottom of their bodies and walking on the tips of their tentacles.  This would be a fun behavior even if that was all they did.  However, after wandering across the seafloor with the coconuts, the octopusses upended the shells they carried and climbed underneath them, using them as hiding places. Some even pulled two halves together, completely enclosing themselves inside (see photo)!  This would be an interesting behavior regardless of the greater implications, but it’s even more exciting when you consider that few invertebrates have been observed using tools.  Because the octopusses are carrying the coconuts with them deliberately and then using them, the research team believes that this is a clear demonstration of tool use by an invertebrate.

I think this is an amazing finding, so I hope you’ll watch the video the researchers made available.  It’s only a couple of minutes long and it’s well worth the time!

There is also a great story about the finding on the NPR website that has some more pictures.  It can be found here:

http://news.nationalgeographic.com/news/2009/12/091214-octopus-carries-coconuts-coconut-carrying.html

Discoveries like this remind me of why it is great to be a biologist and how amazing nature really is.  Ultimately, what’s not to love about a coconut-carrying octopus?  :)

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Text copyright © 2009 DragonflyWoman.wordpress.com

Making a naturalist’s adventure pack

As part of one of my jobs, my coworker and I spend one day a week on a boat at an urban lake in Tucson.  The lake is an urban fishery, so we sample the water and make sure it has the qualities that fish require to survive.  It can be a really awful job at times, but there are definite perks.  One of the best is the wildlife that we get to see at the lake!  Last summer, I posted about the dragonfly swarm we saw at the lake.  We see tons of water birds that we wouldn’t otherwise see.  Tucson isn’t exactly known for its abundant water, nor its heron, egret, and pelican populations, but we see them all the time!  That sort of thing makes the job worth it, even on really hot summer days.

Lakeside Lake, Tucson, AZ

Lakeside Lake, Tucson, AZ

My coworker and I are both field biologists and naturalists.  This means that we make scientific observations of the natural history of biological organisms in their natural environments.  We love observing nature!  Unfortunately, we don’t know everything about every plant and animal we see at the lake.  I study insects and my friend studies fish and snakes, so neither of us are good at identifying some of the other things at the lake, such as the birds we see.  Several weeks ago, we came up with the idea to make a pack full of the tools we need to be better naturalists during our time at the lake, and the Naturalist’s Adventure Pack was born!  I thought I should post about what went into our pack so that all of you might be inspired to make your own.

Mountainsmith lumbar pack

My Mountainsmith pack. Photo from mountainsmith.com.

First we chose a container for our gear.  I happened to have an extra Mountainsmith lumbar pack at home, so we selected this as our pack.  It’s roomy, durable, and comfy to carry, the characteristics that make a good naturalist’s pack.  I personally love and recommend the Mountainsmith lumbar packs.  They’re expensive, but they last forever and have an excellent warranty.  If you don’t want to buy a new pack though, just use whatever you have lying around at home – so long as it’s durable and comfortable to carry.  You’re not going to use your naturalist’s pack if you have straps digging into your shoulders painfully, so comfort is really important to consider when choosing a bag.

digital camera

My beloved Coolpix, soon to be retired... Photo from dpreview.com.

The first thing that went into our bag were tools for documentation of the things that we see.  These are the most important things a naturalist can carry!  We added a high quality notebook (acid free is best) and some good waterproof pens for recording observations and making notes.  We threw a small point-and-shoot digital camera in.  I’ve got an old Nikon Coolpix 995 that does still photos and short videos so we can visually document the things we see.  You can write all the notes you want, but when it comes to natural history, a picture really is worth a thousand words!  Sometimes people simply won’t believe you if you don’t have photographic evidence.  If you don’t want to carry a lot of stuff with you, a notebook, some pens, and a camera are all you need to make a basic naturalist’s pack.  These simple tools are enough to make high quality observations.

Sibley Guide to Birds cover

The Sibley Guide to Birds. Image from Amazon.com.

Because we aren’t able to identify everything at the lake, my friend and I added a few key field guides to our pack.  We are both bad at birds, so in went the bird field guide I’ve had for ages.  We use a small, simple field guide, so it doesn’t have everything in it, but it’s good enough for our purposes.  If you want something better or you are a more serious birdwatcher, the Sibley Guide to Birds is quite popular among birders.  We also put a dragonfly field guide in our pack because there are a lot of dragonflies at the lake.  Even though it’s a bit heavier than some other options, I chose the excellent Dragonflies of the West because it contains both dragonflies and damselflies and is specific to our region.  When choosing your field guides, I have a few recommendations.  One is to make sure that you’re not carrying so many books or such big, heavy books that your pack is going to become bulky and uncomfortable.  Like I said earlier, if your naturalist’s pack isn’t comfy to carry, you won’t want to use it.  Second, consider only carrying the field guides for the things you are most interested in and/or the things you have the least knowledge of.  If I had my way, I would carry bird, dragonfly, butterfly, general insect, mammal, tree, flower, and mushroom field guides with me everywhere, but it’s way too much to carry.  So, I bring only the guides I know I’ll use.  For the lake, that means only birds (because neither of us know them very well) and dragonflies (because there are a lot of them at the lake).

Sometimes you’re going to be too far away to see something well enough to identify or properly observe it.  Conversely, sometimes things are too small to observe easily with the naked eye.  This is where some simple optics tools come in handy.  My friend and I put a pair of inexpensive binoculars in our pack (these were extra inexpensive since they were a hand-me-down from my sister!) so that we could see birds and dragonflies from far away.  I’ve also included a magnifying glass to use with insects.  There are other things you could carry with you, from field-use microscopes and loupes to multi-thousand dollar binoculars and spotting scopes.  Choose the tools you think you’ll use, you can either afford or already have, and make sense for your environment and strength.

collapsible insect net

Collapsible insect net, folded. Image from Bioquip.com.

Last, consider including some specialized equipment that is appropriate for your favorite plant or animal group or your particular interests.  I’m an entomologist, so I put a bunch of insect gear into my naturalist’s pack.  I’ve got glassine envelopes for holding butterflies and dragonflies, plastic bags for other insects, a strainer for scooping bugs out of water, and a collapsible butterfly net.  (You can get all of these things except the strainer from an entomological supply company called Bioquip.  My strainer is a simple soup strainer from Target!)  My friend is a reptile expert, so she sometimes carries her snake stick with her.  If you’re a plant person, a small plant press would be an excellent way to make a leaf or flower collection on a hike.  Birders sometimes like to collect feathers, so a plastic envelope can come in handy.  There are a lot of artist-naturalists out there and they will carry watercolors, colored pencils, or markers along with a good sketchbook and draw or paint things in the field.  Think about the kinds of things you like to watch the most and the things you’ll need to collect and/or observe them.  Then choose your specialized gear accordingly.

Our naturalist’s pack is great!  We’ve enjoyed our new ability to figure out which birds are on the lake, visually record the behaviors of the pelicans eating fish, and make note of our observations.  Our pack fits all of our needs.  It’s big enough to hold all of our gear, but it’s still comfortable to carry.  Our pack is heavy, but not so heavy we don’t want to use it.  It’s got almost everything we could want in the field, but it doesn’t have a lot of extra stuff we’re never going to use to weigh us down.  I’m sure we’re going to get a lot of use out of our naturalist’s pack and it has already greatly added to our enjoyment of the lake.  If you like observing nature and spending time outdoors, I highly recommend you make your own naturalist’s adventure pack!  You won’t regret it!

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Text and Lakeside Lake image copyright © 2009 DragonflyWoman.wordpress.com.

Animated science!

I was going to post about another subject this week, but I came across some great information last week that I’ve been dying to share.  So, we interrupt your regular broadcast for this special report!

I was working on my previous blog post just before Thanksgiving when I heard an NPR Morning Edition report about ants.  In it, the Morning Edition science correspondent, Robert Krulwich, discussed a paper by researchers from the University of Ulm that was published in the journal Science in 2006.  The researchers discovered that ants in the Sahara likely count their steps to find their way back to their nests after they forage for food, remarkable findings that were widely broadcasted by the New York Times and other newspapers and bloggers around the world.  Krulwich’s report was about the ingenious experiment the researchers did to confirm that the ants might be counting their steps.  At this point, the ant story is two years old, old news that has been rehashed several times, so I was a little surprised that Krulwich was reporting about it at all.  Still, I went to the NPR website to see the animated video the reporter mentioned at the end of his segment just because I was curious what they’d done.

I have to say that I was completely blown away by the video!  It is one of the absolute best presentations of science I’ve ever seen.  The video is a short animated piece that is simple to understand, very brief, and accurately depicts what the scientists did and how they came to their conclusions in an entertaining format.  Its simplicity and level of approachability is amazing.  If all science was presented to the public the way NPR presented this ant study, it would be very easy for everyone to understand what scientists do!

I highly recommend that you check it out, if only to see a really great presentation of scientific information.  The ant story itself is pretty good too.

We now return to your regularly scheduled broadcast…

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Text copyright © 2009 DragonflyWoman.wordpress.com.