Panther Pond has recently (?) been populated by Chinese Mystery Snails. Actually, I don't know how recently this happened. They first became obvious in my part of the lake in 2007. You can learn more about them here, or, of course, just search the Web for "chinese mystery snail."
Are they a problem? Nobody really seems to know. The best guesses I've heard are that they'll probably displace our native snails, for whatever ecological problems that might cause; and they may carry parasites like swimmer's itch. They seem to be far more numerous than the native snails, so does that mean more cases of swimmer's itch? The studies haven't been done yet.
Are they good to eat? Supposedly they were originally brought to this country as a food item, but I haven't eaten one, and I'm not about to. If you try it, let me know how they are.
Can they be controlled? I doubt it, just judging by the number I see out in front of my house. I'd estimate the distribution is something like one per square meter at this point. I've scuba'd out to a depth of about 25' and they're all over the bottom out there, not just on the rocks near shore. The article referenced above mentions various control methods, but I doubt any of them would really have much of an impact, and they all have their own risks. You can certainly throw any that you find up onto the shore; but there are so many of them that it'd be just a "drop in the bucket." (And if you throw out too many, they'll probably create a pretty good stink for a while.) Just as a matter of curiosity, and, mind you, I'm not recommending this, I tried smashing a couple of the snails on a rock under water, and small fish ate the exposed snails in very short order. Of course, that left a lot of sharp shell fragments under water, so it's not a good thing to do where people are swimming. And, again, it'd have an insignificant impact on the lake's population.
July '09 - I spoke with Bob French. He's of the opinion that there are fewer snails this year than last, and wonders if some local critter has learned to eat them. (Muskrat?) Dunno, in front of my place, I think they're thicker than ever, at least out to a depth of about 20'.
July '10 - The plot thickens - There are still plenty of snails out there, but now I'm finding clusters of up to 3 dozen or so empty shells, in water about 5' deep. Every one of the empty shells has had its pointy end broken (bitten?) off. It looks as if some natural predator has developed a taste for snails. But which one? The evidenece hints at something with sharp teeth and a long, twisty tongue. Muskrat? Turtle? Fish?
In fact, practically all the live snails I can find this year have had their tips abraded, as if something had gnawed on them, but not broken through. That would appear to exculpate the muskrat. It must be something pretty numerous and pervasive (unless this is a normal part of the snail's cycle, which seems unlikely)?
7/30/10 Migration or predation? There aren't many snails out front now. I can still find a few live ones, but very few compared to even a month ago. So I checked some deeper areas. Below 15' there are a lot more snails, and the deeper I went, the greater the proportion of live ones. At 25' +/- it's nearly all live snails, and they look a lot healthier than the ones close to shore. I hit the thermocline around 28', and there were no snails at all beyond that.
7/31/10 Up the Tenney River, on a mudbank close to the water, we found a couple of clutches of badly chewed-up empty shells.
9/1/10 A muskrat has been using the bottom of our float for a dining area. It's covered with grass (why grass?) and mussel shells. But I also found one snail shell. It's been opened from the bottom, not the top, but it suggests that the muskrat might be at least one of the things that's eating the snails.
There's a fresh batch of healthy-looking snails near shore now - maybe the cooler water brought them back in?
July 2012 - There are still snails out there, but nowhere near as many as we had in '08 - '09. Something must be finding them tasty.
July 2014 - LOTS of snails in close to shore. With the water as warm as it is, they should be moving out to deeper water. Marie reports seeing ducks eating the snails. Go ducks!
August 2016 - I watched two sunfish taking turns grabbing a snail and shaking it, like dogs with a stuffed toy. I couldn't get close enough to see if they were grabbing the edge of the shell or the operculum, or whether they were actually getting anything edible off it.
The Voice of Experience: Don't touch the floating snails; you'll regret it.