It fills your shoes, ruins the kitchen floor in the summer and gets in your food at picnics.

But whoever thought of sand as a commodity?

On the Vineyard sand is emerging as exactly that, right up there with gold futures and pork bellies, as towns and private groups compete to get their hands on the stuff to use as ammunition in their ongoing battle against erosion.

The value of sand has skyrocketed, and given all the predictions that global warming will cause a rise in sea levels, it’s unlikely to come down anytime soon.

Leading a tour of the Sengekontacket, Felix Neck guide Emily Smith rounded Sarsons Island Friday in her red kayak and stopped. Something in the pond had caught her eye. She backtracked, peered into the water for a few moments and then pulled out a horseshoe crab. The kayakers on the tour crowded around for a look, bumping their boats together as they packed in. She flipped the crab over to show its small legs squirming in the air and began spelling out facts about the creature.

In a 1952 aerial photograph of Sengekontacket Pond that hangs behind the door to Augustus Ben David’s World of Reptiles And Birds in Edgartown, you can count two properties — the one you’re standing in and the Felix Neck Wildlife Sanctuary. Today Mr. Ben David estimates that the homes clustered along the shoreline number in the thousands.