Friday 5: Dragonflies Getting Busy

It is still cold in many parts of the US.  In fact, it even snowed in Tucson last weekend!  Having moved to Arizona from somewhere much colder, I know that winters can be dreary and sometimes it seems like the spring will never come.  So, let’s think about the good things to come in the spring and summer instead!  Today’s Friday 5 is all about something that’s coming soon to an area near you: dragonflies getting busy and making babies!

Step 1: The male finds and defends a territory.

defending territory

A male blue dasher (Pachydiplax longipennis) defends his territory from a perch.

Like many animals, male dragonflies attract females by showing off.   To have any chance at success in convincing a female to mate with him, a male dragonfly has to show how amazing he is by finding a good place for egg laying, setting up a perimeter around that area, and defending the space within that perimeter from other males.  This is hard work, but the males who defend the best territories tend to get the most girls, so it’s worth the effort.  Some dragonflies fly within their territories nearly constantly (these are “fliers”).  Others find perches within their territories (the “perchers”) and only fly when their territory is threatened by another male, or when they progress to Step 2.  (For more info on dragonfly territoriality, check out part II of my dragonfly trilogy for a whole post on the topic!)

STEP 2. The female flies into the area.

And all hell breaks loose! Dragonfly males may spend hours each day flying around in their territories, and it’s all in preparation for this moment.  It must be terribly exciting. When a female flies into his territory, the male will fly out toward her and try to grab her. If he is successful, he moves to Step 3.

Step 3: The male grabs the female.

male grasping female

A pair of desert firetails (Telebasis salva) shortly after the male has grabbed the female.

Success!  As you can see in the photo of the damselflies above, the male grabs the female behind the head.  Males need to get a firm grip because other males might try to steal the female from him and this is probably the best place to hold on.  This means that the male is grabbing the female with the section of his body where his sperm are produced, so he has to transfer sperm from the genitalia at the back end to a secondary set of genitalia up near the thorax before he grabs a female.  (Scroll down to the lower part of my post on why dragonflies are the best insects for more info on this and a photo of the two sets of genitalia.)  Females can refuse to mate with a male, even after he’s grabbed her.  If she’s unwilling, the male will eventually let her go her own merry way.  If she is willing to mate, they progress to step 4.

Step 4: The pair assumes the “wheel position” and mates

mating dragonflies

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

To transfer sperm to the female, the male has to bring the genitalia at back end of the female into contact with his secondary genitalia near his thorax, all while maintaining his grip on her head.  He curls his abdomen under so that the female is held mostly parallel to his body.  She then curls her abdomen up toward his secondary genitalia.  In the process, they form the wheel position, this awkward looking position that looks like a circle drawn by a toddler.  Some dragonflies, such as the dragonflies in the photo, continue to fly in the wheel position and others land while in the wheel position.

Males are super competitive with one another when it comes to females, even at this stage.  If he is to be the biggest, baddest male at the pond (or stream), he needs to father the most children.  If a female has mated with another male before him, there’s a chance that the other male’s sperm is still stored in her sperm storage organ and might fertilize some of his gal’s eggs, even after he’s mated with her himself.  No problem!  Many male dragonflies have genitalia designed to scoop sperm out of females before he deposits his own.  Others do some really amazing things.  My advisor shows a video in his insect behavior lecture that shows a dragonfly in Germany that grabs the female and immediately whips her whole body around in a somersault, flinging the sperm from her body in the process!  Basically, males are selfish.  They want their offspring to be the only offspring in their territories and removing sperm deposited by other males from their mates before transferring their own sperm into the female helps ensure that this is realistic.

So the dragonflies get it on for a while.  Then they move on to Step 5.

5.  The female lays her eggs.

Anax laying eggs

A pair of common green darners (Anax junius) laying eggs. The males guards his female from usurpers by maintaining his hold on his mate.

Now that the male has successfully held a territory, encountered a female, and encouraged her to mate with him, there’s only one thing left to do: lay eggs!  However, there are a lot of males around the pond (or stream) and very few females, so other males may try to grab the female and mate with her before she finishes laying her eggs.  If that happens, they’ll remove the freshly deposited sperm and replace it with their own.  So a male who just mated with a female often guards her while she lays her eggs.  Guarding takes many forms.  Some males release their hold on the female and fly above them.  Others let the female go, return to their perches, and fly out to fight any potential usurpers.  Many species keep their hold on the female until she has finished laying her eggs, as in the green darners in the photo.

Egg laying habits vary from species to species too.  Some species fly over the water and dip their abdomens into the water several times, releasing eggs each time.  Some stay in one place, holding onto a rock or piece of vegetation, and lay all of their eggs in one spot.  Still others crawl all the way underwater to lay their eggs!  Many species just spray their eggs into the water and let them fall where they may, but some stick their eggs to rocks or vegetation or embed them into emergent plants or algae.  There is a lot of variation in egg laying and mate guarding behaviors, but they all accomplish the same thing: ensuring that the eggs a female lays in a territory are mostly those that have been fertilized by the male holding the territory.

When it warms up and the dragonflies come back out, I encourage everyone to find a pond or stream nearby and settle down to watch a little dragonfly porn.  Dragonfly mating habits are fascinating to watch!  You won’t be disappointed.

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Unless otherwise stated, all text, images, and video are copyright © 2011 DragonflyWoman.wordpress.com

Color Polymorphisms in Dragonflies

In my last post, I talked about the dragonflies that my fiancee and I saw on our recent photographic trip to Sweetwater Wetland in Tucson.  We took a lot of photos of dragonflies and as I went through them, it occurred to me that there is an important topic related to identifying dragonflies that I have not covered so far in my blog: odonate polymorphisms.

If you’re like most people (including me until I’d been an entomology grad student for almost a year), you’re now thinking to yourself, “what is a polymorphism?”  You probably already know more about polymorphisms than you might think!  First, let’s take apart the word to define it.  The root “poly” means many.  Think back to geometry and polygons – a polygon is a shape with many sides.  The root “morph” means shape or form.  So, the word polymorphism effectively means “many forms.”  Form can refer to shapes, colors, sizes, and other characteristics of biological organisms that might vary between stages, sexes, or individuals within the same species.

You probably know about a few species that exhibit polymorphisms already.  Birds are a classic example of sexual dimorphism (di = two, so dimorphic species exhibit two forms): males take one form while females take another.  In birds, the males are often one color while the females are another.  In most cases, the males attract the females, so the males are the more colorful, showy individuals.  In general, the more brightly colored males are healthier and better able to produce strong offspring with a high chance of survival, so females will choose mates that are brightly colored over less colorful males.

Peacock and peahen

Peacock and peahen

As an example, consider peacocks.  Peacock males are VERY showy with their long, elegant tails while the female peahens are much less colorful and have much shorter tails.  Peacocks with the biggest, baddest tails get all the girls while the less showy males have to settle for leftovers (sometimes younger or less healthy females) or simply cheat their way into getting a mate.

Other animals that show dimorphisms are deer and elk.  Again, the males are trying to attract the females and are willing to fight other males for them.  Elk or deer with big racks are generally better able to successfully fight other males.  As in birds, the buck with the biggest rack is likely healthier than the bucks with smaller racks – they have to be getting enough food and other resources to grow those antlers in the first place.  The doe chooses her mate from the available males and usually selects the one that is best able to win fights, the one with the best antlers.  Because the females are not fighting amongst themselves and are not trying to attract the males, a doe doesn’t need antlers.  So, some elk and deer have horns (the males) and others do not (the females).  They are also sexually dimorphic.

Now let’s get back to the dragonflies.  Like in birds, elk, and deer, it is the role of the male dragonflies to attract female dragonflies if they wish to produce offspring.  Thus, male dragonflies are often much more brightly colored than the females and many species are sexually dimorphic.  Take, for example, the blue dashers, or Pachydiplax longipennis.  If you follow my blog, you’ve seen this one before, but here he is again in all of his elegant glory:

Blue dasher (Pachydiplax longipennis) male

Blue dasher (Pachydiplax longipennis) male

Blue dashers are very common mid-sized dragonflies across a big section of the United States, including Arizona.  The males are easy to identify based on their bright green eyes and the bluish coloration of their bodies.  The abdomen is covered in a waxy substance, or prunescence, which can give them a bit of the whitish look you see in the male pictured here.  Blue dashers are perchers, so you’ll commonly find the males sitting on emergent vegetation or on bushes and/or other plants alongside lakes and ponds.  They sit and guard their territories from their perches, waiting for females to come into their areas so they can mate.  In contrast, the females are known to spend a much greater part of their time away from water and only come to the water to mate and lay eggs.  I found this female sitting on a tree branch far from the water:

Blue dasher (Pachydiplax longipennis) female

Blue dasher (Pachydiplax longipennis) female

Can you see how different the female looks compared to the male?  The males are a whitish bluish color while the females are largely black!  The female blue dashers are about the same size and of similar shape compared to the males, but they have very different body colors, making this a dimorphic species.  Female blue dashers are also very easy to identify.  Just look for a black abdomen with yellowish or brownish stripes on each section of the abdomen.  The abdomen tends to be a bit stumpy compared to the male abdomen, so the wings look disproportionately large.  In fact, this is the origin of the species name longipennis, which means “long winged.”

Blue dashers are considered dimorphic because there are two main forms, but they are not exactly sexually dimorphic either.  Odonates are not sexually mature when they molt from nymph to adult and require a period of a few days to complete their maturation.  Immature individuals, including the males, look like the females.  So, the mature males are blueish and the immature males, immature females, and mature females all tend to look like the picture of the female.

Many dragonflies and damselflies follow similar patterns.  Green darners (Anax junius) are actually polymorphic:

Anax junius mating pair

Green darner (Anax junius) pair

As you can see in the photo, the male (the dragonfly in front) is green and blue while the female is green and green-brown.  Immatures of both sexes can have a reddish abdomen and the females can have brown sections on their abdomen.  Sometimes the females even have about the same blue on their abdomens as the males!  Because the green darners have so many different color patterns, they are considered polymorphic.

Not all dragonflies exhibit dimorphism or polymorphism.  Some dragonflies are monomorphic (mono = one) such that all indviduals look about the same, regardless of sex or age.

Next time I’ll post some more photos from the Sweetwater trip and go over how to identify them.  I hope you’ll stay tuned!

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Text and images copyright © 2009 DragonflyWoman.wordpress.com

Dragonfly sighting!

I was planning on discussing the differences between adult dragonflies and damselflies in this post, but I can’t reist talking about a dragonfly I saw on Saturday instead.  This lovely little dragonfly is Pachydiplax longipennis, also known as the blue dasher:

Pachydiplax longipennis

Blue dasher (Pachydiplax longipennis)

Isn’t he gorgeous?!  Pachydiplax longipennis is a very common dragonfly in the Tucson area, medium sized (a couple of inches long) and usually found perching on vegetation near ponds.  As you can see, the males have a sort of whitish waxy coating over blue bodies (they are pruninose) and they have bright green eyes.  The extent of the pruinosity varies a bit from place to place, but here in Tucson it covers most of their bodies.

This particular male was perching on the bush next to my fiancee’s car (more about why he was near the car in a moment).  Dragonflies (not damselflies – see my next post to learn how to tell the two apart!) are generally split into two groups based on their behaviors.  Perchers, like Pachydiplax longipennis, sit on vegetation near water.  From their perches, they are able to protect their territories from other males, see females that come into their territories, and spot insects and other animals they might want to eat.  When disturbed for any of these reasons, they’ll dart off their perch and fight, mate, or grab their prey, but they spend a majority of their time sitting on their perch watching and waiting for things to happen.

The other group of dragonflies is made up of the fliers.  These dragonflies fly almost constantly, patrolling their territories for mates, aggressors, or prey on the wing.  They rarely stop moving unless they are mating or wrestling with a particularly large piece of food.  You would be hard pressed to get a photo like the one above if this dragonfly were a flier instead of a percher because they rarely sit still that long.

Back to why this dragonfly was near the car.  Dragonflies have amazing vision which they use to find territories, mates, and food.  See those giant eyes that take up almost the entire head of the dasher pictured above?  These are clearly very visual animals.  Dragonfly nymphs are aquatic, so their eggs need to be laid either in or near water.  So, dragonflies need to be able to find the water.  They do this by looking for certain patterns of polarized light as they fly overhead.  If a male finds the right pattern of light, the one that screams “Water!” at him, he’ll set up a territory and protect his patch of the water from other males in the area.  If he’s a percher, he’ll find a nice place to rest nearby and survey his territory from his perch.  Why, then, was this dragonfly near a car?  The clear coating on many cars gives off the same pattern of light as water in ponds.  As far as this dragonfly is concerned, the car is a pond!  He thinks he must protect it from other dragonflies that might be in the area, so he was perched in the bush nearby and watching the area around the car.

This dragonfly exhibited one other behavior while I watched.  This picture is unfortunately not as clear as it could be because he was having a hard time staying still, but you’ll get the idea:

Pachydiplax longipennis obelisk

Blue dasher (Pachydiplax longipennis), obelisk position

This dragonfly is in what is called the obelisk position, sitting on the antenna of my fiancee’s car.  Have any idea why they might rest in this position?  I’ll give you a hint: this photo was taken around noon on a hot and sunny day.  Dragonflies actually use this position as a way to help cool their bodies down when they are overheated.  Dragonflies, like all insects, are cold blooded (=exothermic) and their body temperature closely tracks the temperature of the air.  When it is very hot or very sunny, their body temperatures get too high and they must use a variety of behaviors to cool down.  Dragonflies are pretty unique in using the obelisk position.  Here’s how it works.  Imagine you are out under a very hot sun.  You have two choices of positions: standing upright or lying flat on your back.  Which position should you use to minimize the amount of sun that hits your body?  If you chose standing upright, you’re correct!  By standing upright, the summer noon sun will only hit your head and shoulders, leaving the rest of your body shaded.  If you laid on the ground, half of your body would be hit by the sun!  Dragonflies use the oblesik position in exactly the same way.  By extending their abdomens upwards, instead of holding it horizontally as they usually do (shown in the first photo), they minimize the amount of sun hitting their bodies.  The sun only hits the tip of the abdomen, part of the thorax and head, and part of the wings rather than the entire top surface of the dragonfly.  So, this dragonfly is in this position because he is hot and needs to cool down.  If the obelisk position isn’t enough, he’ll fly into a shaded area, even if it means abandoning his territory for a while.  Defending a territory isn’t worth risking death by overheating.

This dragonfly flew away shortly after I took this photo.  I disturbed him enough that he gave up on defending his “pond” and flew away to look for a place that had fewer dangerous large mammals.  I hope he found a backyard pond instead of another car!  I always find the car thing a little depressing.

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Text and images copyright © 2009 DragonflyWoman.wordpress.com