Gross, but Cool! Cannibalism in the Amphibisphere, Bugs, Fish, Etc.
Spent last weekend at a friend’s cottage up near Haliburton, which was a lovely change of pace from the unpleasantness of Toronto in summer. Everybody else swam (I just sat in the boat or on the dock), we had campfires, ate s’mores, and there was lots of lovely wildlife to observe, including hummingbirds, dock spiders, dragonflies, squirrels, otters, fish, ducks, etc. Unfortunately the weather was cloudy for most of the weekend, so despite going during the height of the Perseids we didn’t see many shooting stars — but at least there WERE stars, which is one of those things about living in the city that I find terribly, terribly depressing. No stars at night is awfully unnatural.
On the first morning we were there, I happened to be up and about rather early, and got to see something pretty damn cool while hanging out down by the river: a big bullfrog eating a slightly smaller frog (and having a hell of a time of it, since the smaller frog was probably not quite “smaller enough” and put up a good fight against becoming breakfast).
After her big meal, the bullfrog wasn’t going anywhere fast, so I managed to get some pictures of her basking in the shallows some time later. She actually stayed around for a whole day, and we kept noting “yep, our frog’s still there,” every time one of us went down to the dock. One of my friends had his camera out during the interesting display of cannibalism, but he hasn’t sent me the pictures yet — when I get them, I’ll update this post and share.
Bullfrogs, L. catesbeiana, are one of the more common frogs in Ontario waterways, and may be distinguished from the similar-looking Green Frog by looking for the two ridges that run laterally down the Green Frog’s back (not present on my froggy friend pictured above). Males of the species have a bright yellow throat, and their tympanum (the ear structure of frogs, which appears as a circle just behind the eye) is about twice the size of the eye. So my frog here is likely a female, as her throat isn’t particularly bright, and her tympanum are rather small.
Bullfrogs are uniquely suited to eating larger prey than most other frogs, and stomach content analysis has found that they will commonly eat comparatively large vertebrates, including fish, rodents, small turtles, birds, bats, and (of course) smaller frogs. Basically, they’ll eat anything that they can get into their mouths. While bullfrogs do have teeth, they’re not much good for crushing or cutting up prey animals — like snakes, bullfrogs tend to swallow their prey whole. The teeth are just there for grasping and holding the prey animal in the bullfrog’s mouth.
Bullfrogs, like all frogs, are often considered to be measures of the health of an ecosystem. Frogs are very sensitive to pollution, and will be one of the first creatures to disappear if their lake or river system becomes severely polluted. Unlike most other frogs, though, bullfrogs may also be a pest species, as they are voracious eaters and can easily out-compete (or simply devour) other species of frogs if they are introduced into a new area. Bullfrogs are also considered a delicacy item for human consumption, and if you’ve ever eaten frog’s legs, they were probably the legs of a bullfrog.
Another “gross but cool” critter that we got a good look at during our weekend was Dolomedes tenebrosis, the largest spider found in Ontario. Well, they actually may have been D. scriptus, because the two species are very difficult to tell apart, but I’m guessing tenebrosis because all of the examples we saw were quite dark in colour. Commonly known as “dock spiders” or “fishing spiders”, they (as their name suggests) tend to be found near water, often on docks or fallen trees that overhang the water. Fishing spiders are opportunistic feeders, often preying mostly on the bugs that ride along on top of the water (water striders and the like), but also catching airborne insects above the water, or grabbing minnows and other small critters that swim too close to the surface. Being as large as they are (females may have legspans of 10cm, although males are only about half that size), they can catch quite a variety of prey, including large insects like dragonflies which most spiders would have a very difficult time with.
There were several of the dock spiders to be seen down by the water’s edge, but one particularly interesting individual was this one, who we found guarding her egg sac (which they will carry around in order to protect it from falling prey to other critters, and also to protect it from getting wet and the eggs drowning). The egg sac may contain over a thousand eggs, and she’ll carry it around until it’s just about to hatch, at which point she’ll build a “nursery web” for the hatchlings. Even after they’ve hatched, the mother spider will hang around and guard her babies for some time, until they’re old enough to strike out and take their chances on their own. This individual was missing two of her legs, and it looked to be a recent injury, possibly incurred during mating (a risky business, with spiders, although usually more deadly for the male — it’s not just Black Widows who feast upon their mates). Loss of limbs is, fortunately for her, not a huge problem for arachnids — having eight, they’ve got a few extras to spare in these sorts of situations, and the limbs will grow back with time, although it generally takes several moults before they’ll be fully functional again. At her next moult this spider will form small, rudimentary nubs of legs, that will grow with subsequent moults until she’s got a brand new pair.
While I’m reminded regularly that there is wildlife here in the city, it’s definitely not as obvious or abundant here as it is in less urban areas. I saw a cicada the other day (and got to tell some of my neighbors what it was, and teach them a bit about entomology while we stood discussing this on the sidewalk out front of my building), and regularly observe raccoons as they forage through the neighborhood garbage bins, and squirrels as they run along the fence beside my bedroom window, but there’s distinct limits to the amount of biodiversity one observes in the middle of the city. Getting outside of the city, even just for a few days, was a welcome breath of fresh air and a chance to reacquaint myself with some of Ontario’s wildlife. Hopefully the planned camping trip up to the Bruce Peninsula next month will be just as interesting, with lots more photos to be shared.