Crab or moult? Thirty shells on one strandline
Every year around the end of May the tideline on our sandy bay is scattered with what look like dead shore crabs, sometimes dozens in a few hundred metres. The first spring I saw it, I assumed something had gone badly wrong in the water. This year I paced out one hundred metres of the line on the afternoon low tide and picked up every crab I came to. There were thirty, and twenty-six of them were not crabs at all, only the shells they had climbed out of.
A moult is easy to recognise once you know the signs. It is light, almost papery, and smells of nothing worse than seaweed. The back edge of the shell lifts like the lid of a box, because the crab backs out through that gap when it sheds, and inside, the shell is clean and hollow, with even the thin coverings of the eyes and the linings of the gills left behind. A dead crab is heavy for its size, its shell stays shut, and the smell tells you before anything else does.
The crabs that have just moulted are the ones to leave alone. For a few days the new shell is as soft as wet cardboard, and they tuck themselves under stones and into the weed until it hardens. I found two this week under a flat stone at the edge of the sand, pale and very still, and lowered the stone back over them as gently as I could.
When I do pick up a hard crab, I hold it from behind, a finger and thumb on either side of the back of the shell and well clear of the claws. Never by a leg: a crab held by one leg can let it go to escape, and I have watched it happen. The velvet swimming crabs, with their red eyes and blue-lined legs, I no longer pick up at all. One caught my thumb two summers ago and held on for a long few seconds.
I have started keeping a tally of moults on the same stretch through the year. So far it reads four in April and twenty-six in May. The moults themselves stay on the beach, where the gulls pick them over and a couple of tides break the rest down into the strandline. What I want to know is whether the peak falls in the same week every year or follows the warmth of the water, which means a thermometer reading next to every count from now on.