The female raft spider measures 15 to 22 millimetres, and the male 10 to 13 millimetres. Both are dark chocolate brown to greenish in colour, with a conspicuous white or cream stripe along each side. Young raft spiders are yellowish brown and have no stripe.
Raft spiders are semi-aquatic and live near slow-moving or still water, such as bogs and grasslands where there are small pools. They can be found throughout Europe and Asia.
Raft spiders do not build shelters but sit on waterside vegetation to bask or wait for prey. They have a dense system of sensory hairs and can move rapidly across the surface of the water, submerging to hide from predators. Adult spiders are active between June and August, feeding on aquatic insects, tadpoles and even small fish.