Why do you think a diving spider surrounds itself with a bubble in the water?

water Spiders are just like any other spider. they need oxygen to breathe. since their home is in the water, best thing to do is to bring the air to their home, that way they can breathe.

the way they bring the air down with them is due to special hairs on their abdomen. they catch the air and allow the spider to bring it down with them.