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?
Assuming it is the first, do they breach the surface tension?
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.
For others who might be interested I found this video showing the behaviour: https://youtu.be/hOLbyAzLmbQ
Why is it the opposite? From the description it seems exactly the same.
The snail is definitely "upside down", for the physical force (gravity) wants to separate her from the "ceiling" on which she clings.