Water spiders, also known as diving bell spiders, eat small fish and insects that get caught in the spider's water bell. Water spiders live completely submerged under the water, only venturing to the surface occasionally for oxygen.
The water spider spends the majority of its time inside of a silk bubble called a water bell. This bell is what gives the spider oxygen and helps it catch its prey. Just like an orb spider spins a web to catch flies, a water spider spins a water bell to catch insects and small fish.
When a small fish hits the spider's water bell, the spider will dart out of the bubble, paralyze the prey and pull it back inside of the bell. These spiders also use the bell for mating and laying eggs.