Tuesday, December 28, 2010

Is that a Dragonfly or an Odonate?

I frequently use the term “odonate”; sometimes it’s “dragonfly”; sometimes “damselfly”. Probably not everyone understands the distinction between these labels, so I hope this post will clear things up. Let’s look at these terms and others just to make sure we’re all on the same page:

Odonata: This is the taxonomic order which encompasses dragonflies and damselflies. It essentially means “toothed ones” referring to their strong, sharp mandibles. This term can be modified to “odonatology” (the study of Odonata) and “odonatologist” (one who studies Odonata).

Odonate: A general term for any insect in the order Odonata. I try to use this term when I speak of dragonflies and damselflies collectively or when I’m talking about particular species ambiguously. An “odonatist” is one who has an interest in odonates.

A male Eight-spotted Skimmer (Libellula forensis).
This is an odonate and a dragonfly.
Dragonfly: This term can be confusing since it may be used in a strict sense or a loose sense. In the strict sense it refers specifically to those odonates in the suborder Anisoptera—these are the classic dragonflies (like the Skimmer at right) and it excludes damselflies. You could also say “anisopteran”, but that’s pretty techy for laypeople. In the loose sense “dragonfly” is synonymous with “odonate”, so inclusive of damselflies.

I try to avoid using this term in the loose sense, but sometimes it’s just quicker than  saying “dragonflies and damselflies” when I’m amongst company who may not understand “odonates”. When browsing book titles on “dragonflies” keep in mind that it may or may not include damselflies. The name of this blog, Northwest Dragonflier, is in the loose sense since Northwest Odonater or Northwest Odonatist 
A male Tule Bluet (Enallagma carunculatum).
This is an odonate and a damselfly. Sometimes
it’s a dragonfly depending on the speaker/writer.
wouldn’t mean anything to many potential readers, and Northwest Dragonflier and Damselflier is just unwieldy in my opinion.

Damselfly: This one is much simpler since it only refers to odonates in the suborder Zygoptera (the damselflies, like the Bluet at right) and never includes dragonflies (in the strict sense). Just as you can with the other suborder, you can get technical and say “zygopteran” if you want to put a puzzled look on the faces of your uninitiated friends which is always fun.

So the title of this post is a bit of a joke since dragonflies are odonates and odonates are dragonflies—in the loose sense, anyway.

Wednesday, December 22, 2010

Damselflies Have a Good Head on Their Shoulders

One way damselflies differ from dragonflies is in the head shape. From above a damselfly's head is relatively short (from front to back) and wide with the eyes capping the ends—what could be described as “hammer-headed”. Unlike dragonflies, there is always a gap between the eyes which is at least the width of one of the eyes—usually more. See the image at right which illustrates the distinctive head shape. 

Does this hammer-headed condition give damselflies some sort of advantage? I think it does. Damselflies frequently perch on long, skinny, near-vertical things like grass stems, sedges, and twigs, with the head facing whatever they’re grasping and the abdomen pointing away. The widely separated eyes provide them an unobstructed view around narrow perches, which means they can keep an eye out—well, both eyes out—for whatever they need to look out for. I would guess a narrow perch does not block the damselfly's view at all even though it's right in front of the face.

The photos below illustrate this point. This California Spreadwing (Archilestes californica) was perching on a sedge at the Cottonwood Recreation Area on the John Day River in Oregon. After a few profile photos, he stayed put while I angled around for the front shot. Very cooperative!

Two views of a male California Spreadwing (Archilestes californica) perching on a sedge stem.

What do they need to look out for? Predators are an obvious choice, although I’m not sure how noticeable damselflies are to predators while perching. It must happen sometimes, though. They do often perch-hunt however, waiting for prey to fly within striking range and then taking their lunch back to a perch to finish up. Mature males are also always on the lookout for females, so whatever enhances their view is good for that too.

Tuesday, December 14, 2010

Do Dragonflies Bite or Sting?

I am regularly asked at talks and workshops whether dragonflies bite or sting. The question is posed frequently enough that it is included on a Frequently Asked Questions slide, and I figure that enough people wonder about it to warrant a blog post. This concern doesn’t seem to apply to damselflies necessarily, probably because most of them are small and seem less threatening, but in this post I’m referring to all of them—odonates.

My quick (Tweet-sized) response to this concern over biting and stinging is that odonates do neither to people. If you’re content with the abridged response, you can stop reading, stop worrying about dragonflies inflicting pain, and you’ll be fine. The whole story is a bit more complicated and, I think, more interesting. If you’re curious, continue reading…

Now, it is true that all odonates are predators and that they have formidable, shredding mandibles which make quick work of their meals. If you’ve never looked at the mandibles of a largish species with a hand lens or microscope, you should—they are impressive. It is also true that when you handle an odonate, they frequently reveal their mandibles (by flexing the labrum and labium) and repeatedly open and close them. This is no doubt a reflexive response to being in the grasp of a “predator”.

If those mandibles happen to come into contact with the handler’s skin (particularly the softer webbing between the thumb and index finger), they will close. It is usually more startling than anything else when it happens, but the larger species can inflict a painful pinch and even break the skin sometimes. They will all try it, but the small species (especially the smaller damselflies) have mandibles which are too small to grab the skin and their nibbling feels a little ticklish at worst. When someone receives a painful bite, it is their own fault because they handled a dragonfly in such a way that mandible-to-skin contact was possible.

An ovipositing female Paddle-tailed Darner (Aeshna
palmata). The arrow points at the "stinger".
What about stinging? The females of some odonates are equipped with what could be described as a “stinger”, but this is used strictly for laying eggs—never as a weapon. These are sharp, sickle-shaped blades (known as gonapophyses in geek-speak) which are used to incise an opening in plant material where an egg is inserted. All odonates which lay their eggs endophytically (within plants) have this equipment. This means all of the damselflies and, among North American dragonflies, only the darners and petaltails.

Technically a person can be “stung” by a dragonfly, but it is very rare, and is never committed with the intent of causing pain. This happens when someone’s leg is mistaken for a log or tree stump by a female darner who is just looking for a place to lay eggs. I’ve only heard of it happening a few times, but I would guess that stories of huge stinging dragonflies are more frequent among anglers who often sit along the shores of lakes and streams with bare legs. I have also heard that it is rather painful which doesn’t surprise me.

I have never heard of anyone being “stung” by a damselfly. I presume it is possible, but I think most of them are too small to pierce the skin. The large spreadwings (Archilestes) have hefty ovipositors good for inserting eggs into woody willow and alder branches, and I imagine that they would be up to the task if so inclined.

Several years ago a female darner landed on my jeans just below the knee and started to lay eggs in the fabric. She seemed oblivious to my head and arm movements until I shooed her away—it was interesting and fun to watch, but I didn’t want her to waste her eggs on my denim. I wonder if I would have been a stinging victim if I had been wearing shorts instead, but I like to think that all the hair would have clued her in.

So, that’s the whole story on biting and stinging odonates. The thing to remember is that a free-flying dragonfly will never bite you. Even if it lands on you, it will not bite. Though stinging, technically, can happen, it is extremely rare and it is never done as a defensive or malicious act. Even if you swat at a dragonfly that is too close for comfort (why anyone would do that, I don’t know), it will never bite or sting as a defensive measure as yellow jackets and honey bees might when they are agitated. Odonates will simply fly away.

Tuesday, December 7, 2010

Why now?

It isn’t technically winter yet, but I haven’t seen a dragonfly or damselfly in the Pacific Northwest since the 5th of November (just over a month ago), which is a good enough reason for me to conclude that it is winter around here. It may seem like an odd time of year to start a blog about these insects—when you can’t just go outside and reasonably expect to see one, but it actually seems like a pretty good time to me.

I’m not busy right now looking for and photographing dragonflies and damselflies; I don’t have a backlog of specimens and photos to process and catalog; I’m not making updates to my web site at the moment. I guess I have a little more time to do it right now. Maybe writing an occasional blog post through the winter months will keep others interested until the warmer, sunnier days of spring when they might be able to go outside see some live examples (assuming the weather cooperates). Maybe it will keep my cerebral “dragonfly muscle” exercised through these dark days. Maybe it will just be fun.

Posts on this blog will be all about odonates—dragonflies and damselflies. Topics will range from the very general, which apply to the group as a whole, to particular species. When I write about particular species they will primarily be ones that occur in Oregon and Washington, but I will branch out on occasion and write about more exotic species when the mood strikes me. At any rate, welcome to my inaugural blog post and I hope you’ll be a regular reader.

Until my next post, here's some bright and cheery eye candy:
Symptrum pallipes (Striped Meadowhawk), Sprague River, Oregon, 25 July 2010.