dragonfly

Canada Darner

A few days ago Dan pointed out a dragonfly that was sunning itself on the screening of the window at the front of the house. Or at least, it looked like it was sunning, on the south-facing side with its wings spread. Dragonflies (and all insects) being exothermic, most of their body temperature control is achieved through exposure (or not) to the sun (some insects will shiver, too – you may see this in moths, for instance, on cooler nights).

It didn’t move, though, and I began to think maybe it was dead, the barbed feet still clinging to its final resting place. It did look a bit ratty, with a few nicks out of the delicate wings. It didn’t leave as I approached, or even as I reached out to grasp it. But as I gently folded the wings together over its back there was stiffness, resistance, that wouldn’t be there if the insect was dead. Holding the wings firmly, I lightly pulled on it to see if it would hold on to the screen; it did, and the legs moved feebly once detached.

So it was still alive, just sluggish from the cool night. I took a few photos but left it where it was. Half an hour later, presumably sufficiently warmed, it had left.

The large size of this dragonfly makes it a darner, and the dark body with two diagonal stripes on the thorax makes it a mosaic darner, one of the species in the genus Aeshna. There are more than a dozen mosaic darner species in our area, and they all look confusingly similar. Identification is usually best made with the critter up close or in the hand, but they rarely settle down for long and are frustratingly difficult to catch with a net, while in flight or otherwise. The vast majority of my identifications of this group have been made in situations such as this – sluggish individuals that are easy to get a photo of.

The ID for these guys depends primarily on two characteristics: the shape and colour of the thoracic stripes, and the same of the markings on the abdomen (particularly the segments closest to the body). The eyes can also be useful for species identification. Having the dragonfly in-hand, or having a photo of it, while you ponder the possibilities is really invaluable because it offers you the opportunity to check for small details.

In the case of this one, it has a very distinctive marking that no other species have: that little dot just on the inside of the front thoracic stripe. Also, the sharp hook on the front of the stripe itself. Both of these features identify it fairly easily as a Canada Darner, Aeshna canadensis. The majority of the mosaic darners are not nearly so easily identified, bearing more generic straight slines of varying widths.

I have two dragonfly guides: Stokes’ Beginner’s Guide to Dragonflies and Dragonflies Through Binoculars. I like the photos better in the first, but the species coverage and information are better in the second. There are a few other regional guides in print, some of which are very good, that I simply haven’t gotten around to picking up. At this point, though, I’m waiting for the new Peterson Field Guide to North American Dragonflies by Ed Lam. I’m not certain when it comes out, but Ed was contracted in 2006 with a four-year submission target (I think), which would make it within the next year or so. Ed is painting every single species. Males and females and colour morphs. I can’t even imagine the amount of patience such a task would require! But the guide looks to be beautiful and extremely usable once it’s done. You can check out samples of the illustrations at his website.

Canada Darners are late fliers. They first start to emerge in July, but they can be found on the wing through October, till we get into sustained periods of cold. Some species of darners are migrants, moving south in the fall to warmer regions. Those great swarms of darners you might sometimes encounter during the late summer and autumn might be migrant swarms, feeding before they push on (darners will also simply swarm where there’s really good eats to be had, though, and it can be hard to determine which type a particular swarm is). However, Canada Darners, as far as I know, are not one of the migrating species.

Interestingly, Dragonflies Through Binoculars notes that “this species darkens when cool”. I gather this isn’t the case with all species of mosaics, and would explain why this individual looked so muddy to me. Those thoracic stripes are usually sky blue and yellow-green. The abdominal markings are generally all blue. You can just see the colours starting to come out in the thoracic stripes – if that is indeed what’s happening here – though the abdominal markings remain brownish.

Aside from this guy, the only other dragonflies I’ve seen around in a couple of weeks have been meadowhawks, which seem to be the latest fliers around here, at least in any numbers. Soon, even they’ll pack it in for the year. It’s nice to enjoy these lingering traces of summer while they last.

May Odonates

Sometime last week Dan returned from an outing with Raven to our little pond, saying he’d observed River Jewelwings there. We were both familiar with Ebony Jewelwings, the iridescent green-blue damselflies with all-black wings. River Jewelwings are a close relative, but only the outer half of their wings are black. It wasn’t that I didn’t trust Dan’s observation skills – in many situations he’s far better than myself – but I’ve never seen River Jewelwings, despite having watched for them. Also, what were they doing at our tiny little human-made pond, instead of out along the banks of, say, an actual river? Dan offered to take me back to point out something else he’d found on the same outing (a future post subject – he’s great about finding blog fodder, it’s like having a second set of eyes out there) and we carried on to check out the jewelwings, too.

And yes, they really were River Jewelwings. Delighted, I snapped a few photos before trying to get a bit closer, whereupon they promptly moved down the bank to an area surrounded by brambles. This one’s a male; females look nearly identical, but show a white rectangle (“stigma”) right near the tips of the wings. They’re a widespread species, absent from the far north and deep south of North America, but present nearly coast to coast within the middle band. The Stokes’ Beginner’s Guide to Dragonflies, which has a decent damselfly section as well, indicates that their habitat is “A variety of streams and rivers, especially swift and somewhat rocky streams.” Our little pond couldn’t get much farther from a swift and rocky stream without actually drying up altogether. Baffling. But I wasn’t complaining.

While I was standing there, hopefully waiting in case the jewelwings might come back within lens-reach again, a couple of other odonates settled on the vegetation in front of me. The first was another damselfly, this one a type of bluet. While most of the bluets are blue, not all of them are (some are black, a few are yellow or red; likewise, not all blue damselflies are bluets). In the case of this one, its predominantly black body bore only narrow blue rings around the base of each segment. Unusual among bluets is the fact that the two terminal segments of the abdomen were black, rather than blue. I thought this would make for a slam-dunk identification, but I struggled quite a bit more with it than I thought I would. Bluet identification often requires the examination of their external genitalia, which on an organism this small would require a magnifying glass or a good macro lens (and a cooperative subject). That said, I think this one is possibly a female of either Northern or Boreal Bluet, based on similar photos on BugGuide.net.

Finally, a dragonfly, the chunkier members of the order Odonata. I browsed through both my dragonfly guides, as well as BugGuide, and drew a blank on an ID so I ended up uploading it to BugGuide to have someone else identify it for me. As always, I got a very prompt response, this one suggesting that it was likely a Frosted Whiteface, Leucorrhinia frigida. The species is found throughout the northeast, and appears to be relatively common. My Dragonflies Through Binoculars notes that the male’s thorax starts out yellow and becomes brown with age, and the dark abdomen gradually gets the white frosting at the base that gives the species its name. Their photo doesn’t show any yellow and I presume it’s an older male, while mine appears to be a younger one, which would be why I didn’t see it in the book when I looked. The book mentions that males defend territories of just 1-2 square yards from their preferred perch near the shore. It indicates that males mature (after crawling out of their larval skin) in four days, but doesn’t give any numbers for how long one might live (and defend his territory). I’ll have to look to see if he’s still hanging around in the same spot when I’m next back there.

Leaving behind childhood

Despite living on a lake, I don’t make it down to the water every day, depending on what I’m up to and where I take Raven out for exercise. A few days ago I decided just to take her down to the water to swim, rather than walking her down the road. As I was standing there, waiting for her to retrieve a stick, I noticed the dry husk of a dragonfly nymph’s exoskeleton. In the last few days there’s been dozens upon dozens of dragonflies, skimmers and baskettails and clubtails and even a couple of darners, swirling through the air above our driveway and lawn. It seemed that there was a big emergence just recently, producing all these adults now on the wing. I presumed this exoskeleton to belong to one of them, and looked around to see if I could spot anymore.

Could I ever! At first it was just one, then two. Then a couple more. Then three in one spot. The more I looked, the more I saw. There were dozens upon dozens of exoskeletons clinging to the cattails, the dogwoods, the grasses and tree leaves and shrubs and dock. Dozens and dozens of nymphs creating dozens and dozens of dragonflies. Most were medium-sized and were probably baskettails, but I saw a few larger ones, and also a few small ones that belonged to their cousin species the damselflies.

Dragonflies and damselflies spend anywhere from one month to five years as a nymph, living in the mud and vegetation of lake and pond bottoms, and moulting a dozen or more times as they grow. Once they’re large enough, they climb out of the water and up onto a tall piece of vegetation or other structure. There, they dig in their claws to ensure a firm grip, and then begin shrugging off their skin. Like cicadas, which I watched emerge last summer, they have an incomplete metamorphosis, meaning that the adult insect emerges directly from the exoskeleton of the nymph, without an intermediate stage as a pupa.

As I was poking around the shore, checking out all of the discarded exoskeletons, I heard a rustling. Following the sound, I discovered this dragonfly, still clinging to the reed next to an empty shell. One wing was crimped, and it couldn’t fly. It may have emerged in tight quarters where its wing didn’t have room to expand as it dried, or it may be that its wing got caught in the exoskeleton as it was emerging, and dried at a funny angle. Regardless of the cause, life was done for this unfortunate dragonfly – if it can’t fly, it’s unable to either catch food or mate.