The water spider, Argyroneta, builds its nest underwater and fills it with air!
The bell-shaped nest is made of silk, usually among vegetation. The spider traps bubbles of air, then swims down and releases them into the nest.
When it’s time to breed, the female houses her silk-wrapped egg sac in the underwater shelter.
Water spiders often eat insects that have fallen onto the water, and sometimes they even catch small fish.