Speaking of Nature: Of dragonflies and damselflies: A closer look at their mating habits

This is a column that I have been sitting on for weeks. I was temporarily sidetracked with my exuvia story, but now I’m ready to dive into the nitty-gritty of the life histories of dragonflies and damselflies (members of the taxonomic order Odonata). Today I present you with a photo that perfectly conveys the mating process used by this group. It looks strange at the onset, but as we fill in some of the details it will all start to make sense.

Before I go any further you need to understand that I will be using extremely plain language for this column. The world of insects in general, and of the dragonflies in particular, is loaded with such highly technical language that it can become a distraction from the telling of a story. As an example, here are a few anatomical terms used to describe the heads of dragonflies: prothorax, occipital spine, occiput, ocelli, vertex, fons, postclypeus, anteclepeus, and labrum. That is quite enough of that!

So what we see in today’s photo is a pair of Scarlet Bluets (Enallagma pictum) in a position known as “tandem linkage.” This particular posture is a requirement of the anatomy of dragonflies and the nature of their habitats. All species of Odonata have abdomens with 10 segments. The family we know as dragonflies are heavier and chunkier, while the family we know as damselflies (seen here) are much lighter and more slender. Both sexes have genital openings underneath their abdomens at the position of the ninth segment, which presents a major challenge. How do the members of a mating pair get everything lined up properly?

Well, the excruciatingly subtle differences in the exact geometry of the heads of each species come into play here. At the end of the 10th (and final) segment of the abdomen, males have special claspers that can lock onto the heads of the females of their species. But before locking together in tandem, the males will transfer sperm into a “secondary genitalia” at the base of their third abdominal segments.

The male will lock onto a female and then he will support her entire body weight while she curls her abdomen under his, so that the genital opening on her ninth segment connects with the male’s secondary genitalia and the sperm can be transferred to her.

The pair of bluets in this photo has probably just initiated their tandem linkage. The landscape location where this occurs is charmingly known as “the rendezvous,” and for the bluets this means over the water of a pond where lily pads can be found. The bend in the female’s abdomen shows the segmentation I’ve been talking about and you should be able to imagine her reaching under the male.

You can also imagine her using this flexible abdomen to deposit eggs in the water.Once the eggs are released, they typically float to the bottom and begin to develop. In smaller species that live in warmer, southern areas of North America, this might only require a few weeks. Larger species that live in colder, northern areas might require several years. In this “nymph” form, the insects are fully aquatic and they breathe with gills that are present inside their abdomens, or hanging off their rear ends. In the case of the former, water is pulled in and out of the abdomen in the same way that a bellows will move air. This also gives the nymphs the ability to suddenly expel all of the water at once, leading to a burst of “jet” propulsion; a handy way to escape from predators.

One thing that is nice to know is the fact that both the nymphs and the adults are pure carnivores. The adults prey on other flying insects, while the nymphs generally stick to aquatic insects. That being said, the largest nymphs of some of the largest species might also grab small fish, tadpoles and even newts; basically, anything they can eat. After enough time has passed to allow the nymph grow to full size the nymph will then find its way out of the water and shed its skin one final time. This brings us to the exuvia that was featured in last week’s column, so I won’t go down that road any further this week.

One last thing before I sign off – the name “bluet.” In my library I have a wonderful field guide: “Dragonflies and Damselflies of the East,” by Dennis Paulson. In this guide there are 36 species of damselflies that are called “American bluets” because most of them are blue. Some are miniscule, while others are described as being medium sized, but all of them are very slender and delicate in their appearance. In most species, the males are some shade of blue ranging from a dark, primary blue all the way to a light, powder blue. But, of course, there are always exceptions and the scarlet bluet is an example. The male is red and the female is orange. Only when they are in tandem can one be reasonably sure that they are members of the same species.

So here is your next mission: find yourself a lake or a pond where you can get close to the water’s edge. Then, spend some time sitting quietly and giving your full attention to any dragonflies or damselflies that might be in the area. Males will spend a great deal of their time searching for females (the actual term is “sexual patrol”) and they will be out in the open and conspicuous while doing so.

As long as you are very still there is a good chance that the males will perform all sorts of aerobatics above the water’s surface and you might even catch a pair in tandem. They are out there right now and all you have to do is go look for them.

Bill Danielson has been a professional writer and nature photographer for 28 years. He has worked for the National Park Service, the US Forest Service, the Nature Conservancy and the Massachusetts State Parks and he currently teaches high school biology and physics. For more in formation visit his website at www.speakingofnature.com, or go to Speaking of Nature on Facebook.