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…