Survivors: The Animals and Plants that Time has Left Behind. Richard Fortey

      Turn seawards off Route 1, Delaware, and a century rolls away. A small road soon leaves the commercial strip and the fast food joints behind, as it moves onto flat fields and marshland that still supports scattered, pretty villages lined with white-painted picket fences. This is how much of America’s east coast used to be. The Little Creek Inn is a grander building altogether: a large, foursquare, wooden Victorian farmstead on three floors with shutters at the windows and a fine portico, and inside all polished wood and turned banisters. In the spacious drawing room of the Inn, anticipation is buzzing. The hosts, Bob and Carol Thomas, are serving iced tea to a crew of enthusiasts all dedicated to travelling back much further in time than a mere century or so. This is the chance to come face to face with life as it was millions of years ago. Glenn Gauvry, the local expert, is waving around models of an ancient animal. A small TV crew is there to straighten out their facts before they get down to filming. Two young women biologists have travelled from Canada to see for themselves an event that only happens when the conditions are just right in late May. I am there with my notebook and a fluttering heart. All of us are impatient for darkness to fall.

      Deep in the night along the shores of Delaware Bay the horseshoe crabs are stirring. The tide is now high and there is no moon. Darkness rules, but even in the feeble starlight the overwhelming flatness of the countryside can be made out, except along the rim of the bay where old sand dunes have built up a levee providing foundations for a scattering of wooden beach houses, which loom against the night sky. A path passes between them onto a sandy beach that stretches away into the darkness in a long gentle arc. The shoreline seems to heave with gentle movements.

      First, I notice some very odd sounds. There is a general hollow clattering, a tapping and grinding sound, somewhat like that made by knocking coconut shells together (once used on the radio to imitate horses’ hooves) but altogether less rhythmic, and with a kind of underlying push. Then, as my eyes get used to the darkness, low shelly mounds the size of inverted colanders can be seen slowly pushing and jostling all along the shore and perhaps six metres up onto the sands. Their bumping and clambering together is the source of those tap-tapping percussive sounds. The flash of an infrared torch reveals more details. The head-shield of the horseshoe crab is domed upwards and carries a few weak spines; at its back end a hinge marks a jointed boundary with a second large plate, spiny at the edge, which can flap downwards; and beyond that again projects a stout triangular spike as long as the head, which can waggle up and down. Here at Kitt’s Hummock more crabs are gathered on the mud flats seaward of the sands waiting their turn: strange, green-black, slowly animated lumps. Further offshore again in the shallow seawater tail spikes project briefly above the gentle waves like raised radio antennae and are gone, showing where still more horseshoe crabs vie with one another to get their place on the sand. There are evidently thousands upon thousands of these large animals gathered together in some sort of compulsive collusion.

      One horseshoe crab lies upturned on the sand. Its tail spike waggles feebly, quite unable