Belly down on the grey-tan sand of a south Devon beach, I am turning out sandcastle after sandcastle from a green bucket with a starfish on it, when I notice that the sand is seething with life. “Grasshopper!” my almost-two-year-old daughter exclaims, and she’s half right. The creatures flicking away from my feet, and from the ruins of the sand turret she has taken such pleasure in demolishing, are in fact not insects, but sand hoppers (Talitrus saltator). I scoop one of the housefly-sized crustaceans on to the palm of my hand, and bring it to eye level. Now we are close enough to see the animal’s glistening exoskeleton, its shrimp-like legs, its body the colour of every grain of sand on the beach. For a few seconds the sand hopper lies there, motionless, like a dog half-curled by the fire. Then, with no perceptible movement at all, it vanishes, in a kinetic movement too quick for the human eye. That there are sand hoppers here on this beach tells us that it is healthy. It tells us the shoreline has not been zealously cleaned of seaweed in spring, removing the food the crustaceans depend on. Sand hoppers are also an indication that beaches are free from industrial pollution such as trace metals. They are sensitive to another growing anthropogenic threat, too: nocturnal light pollution. Artificial light, or “skyglow” has been found to interfere with the lunar radar sand hoppers use to navigate the shoreline at night, as they follow the ebb and flow of the tide. They are creatures of the moon, burying themselves in the sand during daytime, and emerging to feed after dark, when the beach is free both of predators and spade‑wielding toddlers. Will the creep of artificial light reach this Devon cove? At its back there is just a single farmhouse, set between two curtains of hillside, studded with wind-turned hawthorn trees. Getting here means navigating a mile-long potholed lane through a deep valley tangled with willow carr. I hope on this beach, at least, the sand hoppers will be free to continue to move with the moon, buried in the sand by day, there for anyone who pauses to notice them.