Snails are pretty cool though with their mucus turning everyting around them friction free so they are badically ice skating. Have no clue what happens in water though.
Do they do this when you put food in the tank? Funny you mention it because I just noticed my snails doing this the other day… it sounds weird but I have engineers come to my house just to see it because they don’t believe it
Is pretty cool to see and all you need is a lamp. Aquatic snails walk under the surface all night. Some fishes vacuum the surface clinging upside down also.
Just to clarify: are your snails walking on the water-air surface upside down? Or they are underwater but clinging to some surface other than the water-air one?
Assuming it is the first, do they breach the surface tension?
They cling to the water surface alone. They cling, they don't "stand" on it. Their whole shell and body is inside the water, and the shell hangs from the body, which is firmly attached to the surface. If I disturb the surface they fall to the bottom.
This is a very common behaviour of pond snails. Just search "snail water surface" on google to see many pictures of it.
The beetle seems to do the opposite thing, though. It is buoyant so it floats to the surface, on which it stands and walks with its legs as it would do on the ground. The air\surface interface is very strong for small critters.
From the point of view of the beetle, he's not walking upside down. Physical forces attract him to the "ground" (the underside of the water surfaces) and he just walks normally, as if he was affected by gravity instead of buoyancy.
The snail is definitely "upside down", for the physical force (gravity) wants to separate her from the "ceiling" on which she clings.
I'd believe that they could hang upside down with their feet at the surface. I wouldn't believe that they could actually propel themselves across the surface; any movement would be due to water currents.
They definitely propel themselves. Even if I stop the filter so that there's no water circulation, they can walk on the surface just as fast as they do on the glass (which is quite slow, but still).
Think about it: water striders propel themselves quite fast on the surface of water, from the other side. The air/water interface is a though barrier to break for small beings. Thus they can use it for support, from either side.
