Mass Emergence: Spiny Baskettails

By May 14th Ottawa had seen a string of six days with temperatures above 20°C, with the last three above 30°C. The warmth signaled the beginning of ode season, with my first dragonflies of the season – both Common Green Darners – seen at the Richmond Conservation Area (May 10) and Sarsaparilla Trail (May 11, 2022). Common Green Darners are migrants, however, arriving on the warm winds flowing from further south. The true ode season begins once it is warm enough for local dragonflies and damselflies to emerge from the rivers and wetlands in which their life cycle began. All odonates lay their eggs in water, and it takes time – from a few months to a few years – for the larvae to go through the individual stages of molting until they are large enough to begin the transformation from nymph to adult. When the nymph is ready, it crawls out of the water onto rocks, emergent vegetation, or nearby tree trunks or plant stems, and then bursts out of the larval shell through a hole in its back, using gravity to pull itself free. I have seen various dragonflies in the middle of this process a few times; I had never witnessed the full transformation as it takes a few hours for the dragonfly to become ready for its first flight. However, when I arrived at Mud Lake on a sunny day in mid-May hoping to find some warblers, it was a mass emergence of at least 50 individual dragonflies that engaged my attention, and I was able to observe many individuals at different points of the process.

I was standing one of the rocky lookouts on the south shore of Mud Lake, and while I was scanning the water for ducks I became aware of several shining pairs of wings in a small shrub in front of me. I noticed three or four dragonflies hanging from the branches of the shrub, then several others in the shrubs growing along the edge of the water, then even more on a dead tree trunk growing out of the lake and even on the vertical surfaces of the rocks! The dragonflies were baskettails, specifically Spiny Baskettails, one of the first species to emerge in Ottawa in the spring. Emerging dragonflies look nothing like the mature adults they will become, but fortunately the Spiny Baskettail is best identified by the shape of its claspers rather than the pattern of colours on its body.

Each dragonfly was hanging from the shell (exuvia) from which it had emerged, and the most recently emerged had translucent, pale yellow bodies with milky wings. Some individuals had not fully straightened out; their abdomen was still curled. It takes time for the new dragonflies to pump haemolymph (their equivalent of blood) through their bodies and the veins in their wings, which in turn causes the body to expand to full size. While these physical changes are occurring inside the body, the bodies themselves are soft and need time to dry and harden.

During this time, the dragonfly’s body darkens and attains it mature colouration. For baskettails, the body becomes black with yellow dashes running along the sides of the abdomen. The wings also lose their milkiness and become clear and transparent, and shiny like Saran Wrap. Once this change occurs the dragonfly begins testing its wings by fluttering them rapidly. After a few minutes it is ready to fly off on its maiden flight!

The last part to change colour is its eyes; it will take a couple of days for them to turn from reddish-brown to green or bluish-green. It is this colour that gives this family of dragonflies its names – the emeralds.

Most of the dragonfly’s life is spent underwater as a nymph, where it feeds on the larvae of various flies (including mosquito), other aquatic insects, and aquatic shrimp. This was the first time I have seen a live nymph; one was walking along the rocks looking for a spot to complete its transformation. The dull brown bug from the bottom of the lake bears no resemblance to the majestic predator of the skies it will become. I picked it up and placed it on the branch of a shrub close by where it wouldn’t get trampled.

Spiny Baskettail nymph

Another nymph was crawling up the thick trunk of a dead tree sticking out of the water, and I spent some time photographing it as it emerged.

In the photo below the dragonfly is hanging upside down from the shell, using gravity to pull itself out of the hole in its back. The thin white threads are part of the respiratory system the nymph uses to obtain oxygen from the water. As an adult, it no longer needs these structures as it obtains oxygen from holes in its abdomen called spiracles. If in doubt as to whether an unmoving nymph contains a living dragonfly or is the discarded exuvia, look for these white filaments emerging from the back.

In the meantime, other baskettails were getting close to taking their first flight.

With so many emerging all at once, it was no wonder that a few found themselves in trouble. I checked the water a few times to see if any had fallen in, and sure enough I found three that needed rescuing. Once a dragonfly’s wings get soaked they are no longer capable of flight, and it may drown if there is nothing to climb up onto. When I saw the ones in the water I grabbed a long stick and gently placed it under the body and lifted it out of the water. In each case the dragonfly was able to grip the stick tightly enough for me to lift it onto land and place it on a sunny branch where it could dry off and warm up.

Drowning isn’t the only danger to dragonflies that have fallen in the water. They may end up becoming a meal for other predators such as birds, weasels, turtles, and even fish. I saw the water churning beneath a thin layer of pond vegetation right next to the tree trunk and was wondering if a turtle’s head would pop up. Instead I saw a catfish swim out into the open, no doubt looking for an easy meal (note the out-of-focus teneral dragonfly hanging just above it).

The dragonflies on this side of the pond were lucky compared to the dragonflies I saw emerging on the north side. When I walked to the small point next to the fence across from the parking lot, I scared off a grackle that already had a couple of colourless teneral dragonflies in its beak. While the dragonflies will become fierce predators themselves once they are able to fly, they are very vulnerable in the first few hours after emergence. It was truly an amazing event to witness so many dragonflies emerging all at once, and I was thrilled to play a small part in helping a few that would otherwise have died make it through the vulnerable transition period.