Odonate Emergence

Black-shouldered Spinyleg

On June 28th Chris Lewis, Mike Tate and I spent some time searching for dragonflies at Bruce Pit and Mud Lake. Mike and I arrived at the Bruce Pit first, and when we heard an Indigo Bunting singing in the trees south of the parking lot we went to get a closer look. Not only did we see the beautiful blue male Indigo Bunting, we also found our first White-faced Meadowhawk of the year. This was a bit of a surprise as the meadowhawks are late-season odes that fly well into September and October….it seemed a bit wrong to find one in June! Chris arrived shortly after this discovery and from there we made our way down into the pit. Cattails had grown up along the southwest corner of the pond, making it difficult to navigate. The Marsh Wrens, however, loved this new habitat…we heard at least four of them singing in the reeds.

Although we hoped to find some Eastern Red Damsels, we didn’t see a single one of these tiny, seepage-loving damselflies. However, as Chris said, as habitats change populations come and go. Hopefully the Bruce Pit population isn’t lost to us forever and a new one will establish itself here in the future.

Four-spotted and Twelve-spotted Skimmers were the most numerous dragonflies while Eastern Forktails and Sedge Sprites were the most common damselflies. I pointed out a Belted Whiteface perching on a stick:

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Belted Whiteface

Then Mike pointed out a damselfly just emerging from its larval shell! Both damselflies and dragonflies begin life underwater, spending anywhere from a few months to a few years in the larval stage, depending on the species. The larvae, called nymphs or naiads, are predators too, and feed on aquatic prey such as small insects, crustaceans, tadpoles and minnows. Like other insects, the larvae have exoskeletons on the outside of their bodies, and molt several times as they grow larger and larger. Once they reach maturity, they make their way to the water’s edge and crawl out of the water onto the shore or make their way up a stalk of emergent vegetation. Transformation occurs when the nymph’s exoskeleton bursts open along the back of the thorax and the adult emerges from the opening.

Damselfly emerging

Damselfly emerging

After emergence, the adult is short and compact with compressed wings. It appears pale and transparent, with none of the vivid colours it will sport as an adult. For the next couple of hours the teneral will pump haemolypmh – a fluid equivalent to blood – into the veins of its wings, causing them to expand. The abdomen lengthens, and the body begins to harden. It also darkens in colour, taking on the colours of a mature adult. Once the wings have dried the teneral odonate will fly off into the vegetation where it can find shelter from predators. The exoskeleton – or exuvia – is left behind.

Damselfly Exuvia

Damselfly Exuvia

We didn’t stay long enough to watch the damselfly go through this process or see it attain the colours of a mature adult. As such, its identity will remain a mystery. Close by we saw the exuvia of another damselfly that had already taken wing. The exuvia of a damselfly can be distinguished from that of a dragonfly by the paddle-like appendages at the end of the abdomen. These appendages help propel the nymph through the water and enable it to breathe by obtaining oxygen from the water. Dragonfly nymphs have internal gills and lack the paddle-shaped appendages. Here is a dragonfly exoskeleton found on a different reed:

Dragonfly Exuvia

Dragonfly Exuvia

Emergence is a perilous time in an odonate’s life. Some odes are unable to break completely free of the exoskeleton and die, trapped in their own larval skin. Others may be blown into the water and drown. Still others may be picked off by predators such as frogs, small mammals, or even other odes while they wait for their wings to expand and harden. I found a few that were struggling in the water and rescued them by scooping them up with the handle of my net and placing them on some vegetation along the shore. Given the amount of bugs – particularly mosquitoes! – these guys eat, every one is worth saving!

After about half an hour of slogging through the water we headed up into the field at the base of the toboggan hill. There were lots of spreadwings perching in the vegetation, mostly Lyre-tipped Spreadwings, with some Slender and Northern Spreadwings as well. I saw something colourful fly by, and was surprised to see a Calico Pennant! I had never seen one here before and didn’t know they could be found so close to home, but Chris said she has seen them here in the the past.

Calico Pennant

Calico Pennant

Another good find was a Black Saddlebags flying high overhead. Then I found something not commonly seen, an odonate that had become the prey of another insect! The predator in this case was a Robber Fly, and it was feeding on an Eastern Forktail.

Robber fly with Eastern Forktail

Robber fly with Eastern Forktail

After leaving the Bruce Pit, Chris, Mike and I went to Mud Lake. The most surprising dragonfly to me was a Stream Cruiser flying about the woods on the west side of the lake. We also found a Horned Clubtail at one of the openings onto the lake, some Dot-tailed Whitefaces, a couple of Common Green Darners, and a few Widow Skimmers, including one perched on a flower overlooking the water.

Widow Skimmer

Widow Skimmer

We proceeded to Britannia Point and walked along the shore toward the ridge. About half a dozen mallard ducklings were sitting on the shore with their mother.

Mallard Duckling

Mallard Duckling

Mike pointed out a pale, almost colourless dragonfly in one of the trees at about eye-level. I took a couple of pictures, but it flew off before we could get a good look at it. The pale green colour indicated a freshly emerged dragonfly, and the eyes were set wide apart, indicating a clubtail of some kind.

Black-shouldered Spinyleg

Teneral Dragonfly

Then Chris found another freshly emerged dragonfly sitting on a rock in the water only a couple of feet away from the shore; it was sitting right next to the exuvia it had just shed. We scanned the area and found a second brand-new adult dragonfly on another rock close by, as well as several exuviae clinging to a couple of large trees extending out over the water! Chris was able to identify one of the fat-bodied, long-legged exoskeletons as that of a Prince Baskettail. She then walked out into the water, and carefully scooped up the exuvia with the dragonfly still clinging to it.

Black-shouldered Spinyleg

Black-shouldered Spinyleg

The thin, thread-like structures left behind in the hole in the back of the thorax are part of the nymph’s respiratory system. They remain attached to the exuvia, and when they are pulled out of the trachea (the tubes that carry oxygen from the outside world to the inner cells of the odonate) during emergence, air is able to flow into openings (called spiracles) along the odonate’s body.

Although the newly emerged dragonfly was not immediately identifiable by its colouration, we could tell that it was a clubtail by its widely spaced eyes.

Black-shouldered Spinyleg

Black-shouldered Spinyleg

Chris was later able tentatively ID it as a Black-shouldered Spinyleg; the exuvia most closely matched the nymph of that species. Other factors seem to fit too, such as the size of the emerged teneral adult, the simple shape of the teneral male’s claspers, and its common status along the Ottawa River. She put the clubtail down on a rock where I took this photo:

Black-shouldered Spinyleg

Black-shouldered Spinyleg

After seeing three freshly emerged teneral dragonflies and several exuviae (larval skins) left behind on the sprawling trees, I dubbed this section of the river “the nursery”. I will definitely be looking out for other emerging odes whenever I come here in the summer.

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