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.
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.
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
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.
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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