Raft spider uses the surface as a net
With a leg span of up to 10 cm, a raft spider can scare most people. The spider, which is one of the largest in Denmark measured by body weight, can often be observed on a lakeshore with its front legs resting on the water surface, while the hind legs stick to the plants on the shore. The water surface is used as a type of replacement for a real web. If a small creature falls into the water from above or approaches the surface from below, perhaps penetrating it, the raft spider’s sensitive front legs will immediately feel the slight vibrations of the water.
In spite of its size, a raft spider can walk, or rather run, on the water, as it speeds forwards to catch the prey, which might be as large as a stickleback or another small fish. The agile hunter gives its victim a lethal toxic injection, bringing it back to the shore, where it sucks all nourishment out of it.
The raft spider makes a rush at the victim, as soon as it feels any water surface vibrations.