Leaving behind childhood

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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.

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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.

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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.

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dragonfly nymph husks on basswood leaves

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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.

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Water bugs

Water beetle

The purpose of the visit to the pond last week was primarily to check out the creatures in the water, not the forest paths, as much as I enjoyed that. We didn’t see any of the salamanders on this trip; as plentiful as the newts had been a couple weeks ago, they were now conspicuous in their absence. In fact, there didn’t appear to be any macro-life in the pond, at least that was visible from the water’s edge. However, there was still lots of micro-life.

We scooped up a number of samples of pond water and bottom-muck, and let it settle out in a basin. Then we poked through it to see what we could find. Copepods were abundant, as well as a number of other little, microscopic creatures that were best observed with magnification. There were also quite a number of large critters, which could be observed easily (and photographed).

The above is a predaceous diving beetle, probably of the genus Neoporus. The group is also sometimes known as water tigers in their larval stages, for their predatory habit, but it also well suits this black-and-orange adult individual. Adults propel themselves with their broadly flattened hind legs, which they use as oars (but don’t confuse them with oarmen or boatmen!). I noticed while trying to get a photograph of this guy that whenever he stopped moving he’d go bottoms-up, with his head tipping forward to point toward the bottom of the tub. It was not especially helpful in getting a good photo, but this is how they collect air to breathe – in tipping forward like this they trap an air bubble underneath their wing covers which they carry with them while swimming. They’re not strictly aquatic; they can fly and will travel in order to exploit temporary water bodies.

Skimmer larvae

This is the larvae of a skimmer dragonfly. Dragonfly larvae, or nymphs, are entirely aquatic during this first phase of their life. Adult dragonflies lay their eggs in the water, usually attached to vegetation, where they develop and hatch. A dragonfly spends most of its life in a larval form. Some species can remain in the water as a nymph for up to five years, depending on the species and the local environmental conditions. During this period they’ll go through more than 20 instars, or larval stages, where they moult their skin to grow. The different types of dragonflies have differently shaped larvae; the skimmers are short and squat, like this guy. Nymphs are predaceous, feeding on other invertebrates, or even sometimes small fish or tadpoles. When they’re ready to metamorphose into adults, they’ll climb up a stem out of the water, where they’ll split their skin and crawl out as an adult form. The newly emerged adult will take a few hours to strengthen up and gain its adult colours.

Blackfly larvae

This is a blackfly larvae. I didn’t know what it was when I first spotted it in the water. It moves along much like an inchworm, securing one end, then moving the other, rather than crawling like a caterpillar, or wiggling like mosquito larvae. It uses suckers on its bulbous end in order to firmly attach to its substrate. If they happen to become dislodged, they remain secured to the substrate by a thin silken strand, much the way a spider that gets knocked or blown off will catch itself on a string of silk before it reaches the floor. This prevents it from getting swept away in the currents, but can also be used as a controlled way to move from one point to another within their habitat. They tend to prefer the faster-flowing segments of streams or creeks, but can be found in ponds as well. A small, leg-like appendage under the head can create a small current where none otherwise exists. They’re mostly filter-feeders, using “gills” near their head to sieve food from the water as it flows past, which is where moving water would be advantageous.

Water strider

I expect that most people will recognize this bug. It’s a water strider (also known by a dozen other names of a similar theme), usually found skittering across the surface of still water such as ponds or lake edges. However, they’ll also inhabit faster moving streams, and in fact this particular one came from the creek where we caught the crayfish, although there were also some on the pond surface as well. Predatory insects, feeding on other insects and invertebrates found on or near the water surface, they can scoot across the water as fast as 1.5 m/s (nearly 5 ft/s) – per second! They need this speed to be able to catch their prey before it takes off. They’re able to stand on the water through a combination of structural and chemical water-resisting features. They have a wax covering on their legs, but the more important factor is a series of tiny hairs with grooves that line each foot and spread out the pressure of their foot on the water surface, while simultaneously trapping air between the hairs, acting a little like snowshoes combined with waterwings. At certain times of year adult striders of some species can develop with wings, which allows them to disperse from one area to the other; in other species they always have wings.

Springtail

This was my favourite of all the little critters we swept up in our container. We got several of these, little tiny guys just a couple millimeters long. They sit on the water surface, much like the water striders. However, to move around, they jump like fleas. In fact, I think the name “water flea” would be much more appropriately labeled to these guys than to the microscopic Daphnia. They jump by using a mechanism similar to the click beetle in yesterday’s post. They have a long spike on their abdomen, resembling a “tail”, which is generally kept locked into place. When they want to jump, they release the clasp and the spike rapidly springs away from the body, pushing against the substrate (in this case, the water), and propelling the insect forward. It’s this jumping mechanism that gives the group its name. They can be found in nearly every habitat, even on the snow surface in winter – these ones are appropriately called “snow fleas”. Interestingly, unlike with the water striders, this speed isn’t for capturing prey, but rather for general locomotion and avoiding predators, as they’re primarily savengers, feeding on decaying plant and animal debris.