Emeralds in the garden

Emerald Spreadwing - male

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.

Emerald Spreadwing - male

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.

Emerald Spreadwing - female

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.

Emerald Spreadwing - female

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.

Emerald Spreadwing - male

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.

Emerald Spreadwing - male and female

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).

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7 responses to “Emeralds in the garden

  1. It’s gratifying to see photos showing damselflies (among other creatures) to be just as beautiful as they appear to the ordinary eye.
    Thanks for explaining just who’s holding whom where during their flying wheel acrobatics.

  2. Well… I have a pretty good damselfly book, but of course it is at work, and I’m not… I’ll try to remember to post the title here. If I forget, send me an email to remind me: jenniferschlick at excite dot com.

    Thanks.

  3. Great post. Excellent photos and informative text.

  4. Here’s a link to the book I mentioned above:
    http://homepage.mac.com/edlam/book.html

  5. themarvelousinnature

    They really are beautiful creatures, aren’t they, LavenderBay?

    Thanks for the book title, Winterwoman. It must not be a readily available title, since it’s not listed on our Canadian bookstore sites. Interestingly, I know that the same author is now hard at work on a good dragonflies guide to be part of the Peterson field guide series, due out 2012. Perhaps he’ll include the damselflies in that guide, as well.

    Thanks, Marvin! Glad you enjoyed it.

  6. Pingback: damsel flies (delicate amongst the reeds) « SwittersB & Fly Fishing

  7. Wow! One day I photographer so well, congratulations.

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