damselfly

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.

When I went out to photograph the wrens, I also poked about the garden a bit. It had rained all afternoon, so all the foliage was damp, but also vibrant. Not much was flying, as far as insect life, and I was mostly looking at the flowers (many of which, after a week of daily rainstorms, were looking a little bedraggled with their heads on the ground). But when I leaned in to the garden edge to peer more closely at something, a cloud of metallic-green damselflies rose from the vegetation, disturbed by my approach.

These may be the first damsels I’ve seen this summer in any numbers. I think I’ve seen the odd one here or there, but not many. Damselflies are the smaller, slimmer cousins of dragonflies, and can be told apart by the general size and chunkiness of their heads and bodies. Also, most damselflies will rest with their wings folded behind their backs, while dragonflies usually rest with their wings spread. These damselflies are the exception, however, and tend to rest with their wings open, though rarely as broad and flat as dragonflies. There are many species that do this, all classified in the group spreadwings.

Dragonflies and damselflies together are part of the order Odonata. There are about 300 species of dragonflies, and 130 species of damselflies in North America north of Mexico. All but two of the 19 North American spreadwings are classified in the genus Lestes. In general they’re associated with the edges of ponds or slow-moving streams. There’s certainly ample water at my parents’, but the garden is some distance from it, so it was interesting to find so many of them there. Many of the spreadwings can be difficult to tell apart from one another, some requiring examination of the genitalia to do so, but I believe these were all Emerald Spreadwings, Lestes dryas.

The females are browner than the males. There are very few species of Odonates where the two sexes are the same or very similar in appearance; generally you can tell them apart fairly readily. However, the surefire way of doing so is to look at the end of the abdomen. Although I didn’t get it in focus in this (or any, as it turned out) photo, you can still get the idea. In males, the abdomen ends in appendages that look like a pair of pincers. These are used to grasp the female gently but firmly around the neck during mating, and two damsels found like this are called “in tandem”. The female has a thicker tip to the abdomen, with a special structure that includes an ovipositor to lay the eggs. The female curves her abdomen around underneath her and touches the tip to a swelling on the underside of the abdomen just behind the male’s thorax (can sort of be seen in the second photo), where she receives the sperm. This is usually called the wheel position, and one can sometimes observe a pair flying together like that.

Spreadwings, like all odonates, are carnivorous predators. Adults have strong mandibles and some of the larger dragonfly species may bite if handled, although it is little more than a strong pinch and doesn’t deliver any venom. They kill their prey by biting it, and “chew” it to ingest it, rather than eating it whole. They eat mainly small flying insects, such as mosquitoes, small flies, and others. The larvae are aquatic, with adults laying their eggs on vegetation, rocks or other substrates at the water’s surface. They look only vaguely like the adults, being not as thin and lacking wings. The larvae eat other aquatic insects, but may even take (very) small fish. Odonates undergo incomplete metamorphosis, meaning they lack the pupa stage that most insects have. Instead, the last larval stage crawls up onto some vegetation, where the skin on the back splits open and the adult climbs out.

Because they’re predatory, both damselflies and dragonflies have excellent eyesight. They have a pair of large compound eyes that are their primary means of detecting prey, but also several occelli across their “forehead” that they use for sensing small changes in light and dark, which helps them to orient upwards. The eyes are another useful feature to separate damsels from dragons – the compound eyes of the latter meet at the top of the head, while those of damselflies are usually widely separated. The eyes are also very important for avoiding predators. Damselflies can be eaten by just about anything larger than themselves. They’re not as strong fliers as dragonflies are, and as a result are often meals for their larger relatives. Adults are also eaten by birds, frogs, and spiders (getting caught in their webs). The nymphs are eaten by larger aquatic insects, amphibians and fish.

Here a male rests on a leaf just above a female. I’m not sure what happened to the male’s abdomen. It’s possible he had a close call with a predator, or when he emerged from his last larval stage his yet-to-harden abdomen was in a funny position. Most insects have very soft exoskeletons when they emerge from metamorphosis. It’s a little like a human baby’s skull – because it has to fit through a very narrow passageway, much of the skull is soft and doesn’t become fully firmed up until the baby is anywhere from nine months to about two years old. In insects the process is necessarily a little quicker – the adult itself may only live a week or two. Insects “wear” their skeletons on the outside, with their muscles attaching to the inner surface, rather than the other way around in vertebrates. The exoskeleton needs to be flexible enough to fit in the cramped space of the pupa or final larval stage, but when the insect emerges, it straightens, wings are expanded by pumping with fluid, and they harden through exposure to air. The air also helps to develop their full colouration, as they are often quite pale when they first emerge.

Unfortunately, there aren’t any really good printed references to the damselflies of North America, which is a funny oversight since there aren’t an overwhelming number of species. Part of the problem is that many can’t be conclusively identified by colouration alone. There are a few good regional field guides, however. In the east, one of the best is A Field Guide to the Dragonflies and Damselflies of Massachusetts, and in the west Introducing the Dragonflies of British Columbia and the Yukon (I’m pretty sure this has damselflies as well, as I recall referencing it while working out there a few years ago – it was part of my employer’s library, but I really liked it).

Tag: damselfly

May Odonates

Emeralds in the garden