One of these things is not like the others

Predaceous diving beetle, prob. Dytiscus cordieri

It was with great anticipation that I put my moth sheet out a couple of nights ago. Although temperature was supposed to peak over the weekend, the moths didn’t know that, and Thursday was the first really warm day we’d had in some time. I was delighted (if not surprised) by a good diversity of moths to the sheet, probably over twenty species once the micromoths are factored in. At least half of the macromoths were new-for-season. Many familiar faces, which is always pleasing.

Another familiar face, perhaps less pleasing to see arrive, was the first Giant Water Bug of the year. Followed shortly by another. And then a third. There were half a dozen or more by the time I shut the light off, all clumsily clambering over the dried grass and dead leaves. A few fell into the window well, where they remained into the next day and following evening. It baffles me that we can get so many of these things at this house, with no water bodies within visible range of the house, when at my parents’ old place I’d see just one or two, despite the big swamp and vernal ponds just a short distance away.

Predaceous diving beetle, prob. Dytiscus cordieri

I was surprised, however, by the appearance of an unfamiliar individual who came to join the party. While the Giant Water Bugs are, as their name says, true bugs, this one was a beetle. Clearly also attracted to light, and, though you can’t really tell from these photos, the broadly flattened hind legs indicate it’s also aquatic (they’re used like oars to propel the beetle through the water). I think this is a species of Dytiscus, perhaps D. cordieri. Telling the different species apart often requires examining the pattern on the underside, though, something I didn’t know at the time I was photographing it.

The largest of these species can be over 4 cm (1 3/4″), though most species are slightly smaller than that, 2.5 to 3.5 cm (1 to 1.5″). They live and feed in fresh water, particularly favouring ponds with emergent vegetation such as cattails or reeds. The larvae are also predaceous and aquatic, and those of the largest species are capable of taking vertebrates such as tadpoles or minnows. Males have round pad-like front “feet” (below), which I presume are used to grip the female during mating.

Predaceous diving beetle, prob. Dytiscus cordieri

Desktop pond

Desktop pond

This week I returned to my parents’ to help paint the exterior of the house. Nearly all of my time over the two days was wrapped up in that, with only a bit of time for wandering about outside, so I didn’t get any photos. The one area I did spend a bit of time looking at was the water garden I mentioned a couple weeks ago. I was looking for Gray Treefrog tadpoles, the possible offspring of my midnight singer, and the garden’s proximity to the house meant I could wander over for a break and poke around.

Peering closely, I spotted a few hanging at the walls of the trough. Tiny and black, their body only a few millimeters, perhaps an eighth of an inch. With their tail, not more than a centimeter, less than half an inch. At this age, I have no idea if they’re treefrogs or another species, though the former seems most likely given the circumstances. Once tadpoles get older, there’s a great identification table put together by a professor at Trent University (Peterborough, Ontario) that I’ll be able to reference, but it won’t be a lot of help right now. For all I know these guys could turn out to be Leopard Frogs, or even American Toads, although I haven’t noticed either hanging around the water garden (that doesn’t mean they couldn’t’ve popped by, however).

Predaceous diving beetle larva

Also while checking out the water garden, I noticed these fearsome looking creatures. There were several, all at least an inch long. They’d hang from the water surface with their head hanging down, I presume breathing at the surface. Mom and I brought one inside to check out more closely; it turned out to be a predaceous water beetle larva. These things are ferocious, sometimes called “water tigers” or “dragons of the pond” for their hunting habits. They’re large enough to take small vertebrates as prey – and this includes young tadpoles.


I really wanted to see what these little guys turned into, and I didn’t feel that they really had a good chance of reaching that point with these tigers in the trough. After some thought and a bit of research, I decided to collect some of the tadpoles and bring them in to let them grow in a protected environment. To that end I grabbed a large, shallow tub, filled it with some of the water from the trough, added some algae and surface plants for food and shelter, and then collected some tadpoles. It was late in the day by the time I did, and I suspect a number were already tucked away at the bottom or in corners, but even still, all I could find were five lonely little tadpoles. I brought the five back with me and they’re now sitting here beside my computer, my own little desktop pond.

Fairy fern and duckweed

I brought two types of plants, which I hope will keep the water well-oxygenated. The red ones on the surface are called Azolla, also known as Fairy Moss, Fairy Fern, Duckweed Fern, and others. They start out green, but when exposed to sunlight turn this striking red colour. Mixed in with them are some bits of duckweed, a commonly-found surface plant on still waters such as ponds. These plants happened to be purchased by my mom; Azolla can’t establish itself in our climate because it doesn’t survive prolonged freezing, but it would be possible to find duckweed on many ponds through our area.

The other type of plant lives below the water surface. I snagged a few clumps of filamentous algae, and there was a fair bit of it on the roots of the Azolla, as well. The algae’s purpose is twofold: first, to provide oxygen, but also, and more importantly, to provide food for the little tadpolets. Algae is one of the tadpole’s primary food sources. Many tadpole-raising websites suggest feeding pureed, frozen lettuce, but it seemed easier just to bring along the tad’s natural food item. It has the added benefit of reproducing on its own, so hopefully I wouldn’t need to keep supplying more of it.

Tadpole eating ostracods

The tadpoles supplement their diet with the occasional bits of protein. The websites I checked were unclear about just what constituted good protein for tadpoles, some suggesting they could get enough from algae, others suggesting you can buy such pellets from pet stores (intended for fish or captive amphibians or reptiles). Well, it turned out I brought some of that, as well.

All those little green spots are little invertebrates called ostracods. They’re bivalved, like muscles or clams, only tiny, and not actually related to the true bivalves. They’re sometimes called seed shrimp for their appearance under a high-powered microscope. To my naked eye (and even to my camera) they just looked like little dark dots, about the size of your average printed period, swimming around in circles.

The ostracods tend to feed predominantly on organic detritus, and indeed the few bits of …stuff (I couldn’t identify what it had originally been) that had settled out to the container’s bottom had clusters of little green ostracods on them. During the afternoon I watched as one of the tadpoles came up to one of the clusters and started chasing and eating some of the ostracods. Guess that’s their protein.

Predaceous diving beetle larva and caddisfly larva

I also had a few stowaways in the Azolla. Here are two critters side-by-side, a very small predaceous diving beetle larva (too small to be a threat to the tadpoles) and a caddisfly larva. The caddisfly has a neat little case made of bits of organic debris as well as what appear to be tiny snail shells. Both were less than a centimeter, maybe a quarter inch long.


There are a few snails in there, mostly this sort of conical type. The snails also feed on the algae, and that’s where I found them all. A number of sites say to avoid bringing snails in with your tadpoles, because they could bring disease, but I figured they came from the same water source, they’re unlikely to be a problem.

Predaceous diving beetle

There are a couple of little predaceous diving beetles in there, adults, little guys. They’re smaller than the heads of the tadpoles. I assume they’re likely to also be feeding on the ostracods in there; there’s not a lot else for them. This may be what the larva, above, will eventually turn into.

Midge larva

Then there’s these guys. I found two of them. I think they’re a type of midge larva. They’d made themselves little homes out of the filamentous algae, kind of similar to what the caddisflies fashion in terms of being a tunnel, but dissimilar in that these larvae weren’t going to be dragging their homes anywhere. They were fairly active, but only insomuch as they would partly emerge frequently from their tunnel and then dart back in. I watched one for a bit and it appeared to be gathering more algae that it would wrap into its tunnel.


This last one was really neat to find. There were two that I noticed, hanging on, it appeared, to the side of the container. It’s a hydra, a type of predatory invertebrate that uses its long tentacles to snag prey. I’ve never seen them outside of my invertebrate zoology classes back in university, so it was really neat to spot these guys. I gather they’re not uncommon; perhaps I’ve just not been looking in the right places. The critter on the left I think might be a type of daphnia, though I’m not sure.


Tadpoles generally take 6-8 weeks or longer, depending on species, water temperature and food availability, to metamorphose into frogs, so these guys may be sitting on my desk for a while. So far they seem to be doing quite well – and I’m finding just watching all the activity in the container to be rather distracting. I may have to move the container to the bookshelf so I can get some work done…

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.


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.