High tide leaves flotsam behind on the beach, at the flood-mark. That's just the spot to find sand hoppers. They usually crawl around under the debris to prevent dehydration during the day. If you stand on or tilt up a pile of old seaweed on the beach, large numbers will jump away. They can 'hop' a distance of 1 meter, so you understand where they got their name. Although you often find them on the beach, they are also good swimmers. There are a several species of sand hoppers found in the Netherlands.