The ants are small enough and light enough that they float because of surface tension. These ant rafts operate on a similar effect to how Gerridae (pond skaters

The ants are small enough and light enough that they float because of surface tension. These ant rafts operate on a similar effect to how Gerridae (pond skaters) walk on the water's surface: https://en.wikipedia.org/wiki/Gerridae https://en.wikipedia.org/wiki/Gerridae The human body is far too dense and large for surface tension based floating to work. Humans can survive reasonably long times in water by employing the Dead Man's Float though.