Dave Bevan / Pair of Sand martins (Riparia riparia) feeding chicks, Carmarthenshire, Wales, UK, July.

David Kjaer / Sand martin (Riparia riparia) juvenile at entrance to nest burrow, Worcesrtershire, England, July

David Kjaer / Sand martin (Riparia riparia) adult and juveniles at entrance to nest burrows, Worcestershire, England, July

Martin Gabriel / Two Giant African snail {Achatina fulica} shells in sand.

Martin Gabriel / Rosy wolf snail shell in sand {Euglandia rosea} from Hawaii

Martin Gabriel / European mussel {Mytilus galloprovincialis} shell in sand. Europe.

TIM MARTIN / Olive Ridley turtle hatchlings on beach in Costa Rica

Martin Willis / Boat near sand island, Sudbury Cay, Great Barrier Reef, Queensland, Australia

Martin Willis / Boat near sand island, Beaver Cay, Great Barrier Reef, Queensland, Australia

Robin Chittenden / House martin (Delichon urbicum) group on ground, collecting sand for nests. Cyprus. April.

Robin Chittenden / House martin (Delichon urbicum) on ground, collecting sand for nest. Cyprus. April.

Dave Bevan / Sand martin (Riparia riparia) flying to nest hole and feeding chick, Carmarthenshire, Wales, UK, June.