Sand Hopper

• It orients itself towards the sea or towards the dune using the position of the sun and the moon, and also the earth's magnetic field, with an internal clock that corrects for the passing hours.
• Its role in breaking down stranded seaweed is so important that the mechanical cleaning of beaches, by removing the wrack, wipes out its populations.
• It is a standard bioindicator of the environmental quality of beaches.
• It is one of the classic models in the study of animal orientation: since the 1950s it has been known that, if moved from its band of sand, it returns by the shortest route using the sun as a compass.
• It has two anatomically separate compasses: a solar one, probably in the brain, and a lunar one in the antennae. If the antennae are removed or painted over it still orients by day, but at night it can no longer navigate by the moon.
• In its antennae and brain it rhythmically expresses circadian clock genes such as period and cryptochrome 2, which points to an antennal clock involved in lunar orientation.
• It also uses the polarisation gradient of skylight, and adults perceive colour gradients better under polarised light.
• Its nocturnal habits are an adaptation to reduce predation and the swings in temperature, salinity and humidity on the beach.

Habitat and environment

Damp sand of the upper beach, beside stranded seaweed

Sources consulted: Wikipedia (es): Talitrus saltator