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

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СКАЧАТЬ 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 to perform the task of turning the body back over again. Five pairs of legs twitch ineffectually in a vain attempt to achieve the same end. I find it impossible to resist the temptation to right the poor animal. It is easy to grasp it by the edges of the head-shield. Once righted again those spindly legs allow the crab to trundle slowly away. Its behaviour seems at once strangely determined, but also apparently random, like the slow progress of a confused old lady on a Zimmer frame.

      Now I see that many of the largest crabs are digging in the sand, their limbs working away beneath the carapace. Some have become almost completely buried, and, although I can detect a kind of deep scrabbling from these animals, they do not seem to be worried by their self-inflicted interment. Other slightly smaller crabs crowd on top of the buried animals. The scrabblers are the females of the species burying their eggs in the sand, while the smaller ones on top are males, competing to fertilise the eggs with their sperm (milt). I realise that there is some kind of order to the apparent mayhem on the beach. A proportion of the horseshoe crabs are paired off, with the lighter male desperately hanging off the tail end of the female, having got a purchase by using his special claspers. However, this right of occupation does not deter other males from having a go at mounting the same burdened female. There is enough of a gap behind the head-shield for some of their interloping milt to have a chance. Much of the clinking noise is a consequence of tussles for dominance. So this gathering of crabs is really an orgy, and an orgy that runs for dozens of miles along the strand, all thickly bordered with scrabbling, lustful animals. As for the poor exhausted females, gravid and overprovided with mates, the moist sand stops their gills drying out, and they may eventually struggle back to the sea when the laying is done – although many do not. Bits and pieces of their carcasses litter the shore.

      I have a better chance to scrutinise the horseshoe crabs closely during the day, although most of them have returned to the sea by sunrise. Coastal Delaware is a land of marshes, with gentle wetlands dominated by the reed, Phragmites, and the cries of wading birds always in the wind. The landscape reminds me of the East Anglian coast in England. Creeks wind their ways inland from the sea, and terminate in small picturesque harbours like Leipsic, where a few fishing boats are tied up to stout piers, with white-painted clapperboard houses landward of the stage. Sambo’s is a restaurant with a view of the creek, and well known for its edible crabs, which are consumed on simple tables covered with newspapers. Eating in Sambo’s is an audible experience with everybody bashing lunch out from shells. It is a place of crunching and squishing and little conversation. Some of the shucked piles are prodigious. There is nothing on the menu about horseshoe crabs. The nearby villages of no more than one or two streets include neat little houses dating back to the 1880s, which is ancient by American standards. Delaware car number plates bear the legend ‘The first state’, acknowledging the fact that it was the first to sign up to the Declaration of Independence. Like several other early American states, but unlike the majority, it is tiny. Nowadays, vehicles on the main roads shoot past; but a mile or two from the freeways little has changed from post-colonial days. I warmed to it immediately.

      After the crustaceous lunch, a visit to Port Mahon shows a few stragglers still on the beach at midday, providing a chance to get close. A large female’s carapace is about 45 cm across. In the sunlight I can readily see that the creature has nearly semicircular eyes set to either side in the midst of the head-shield, topped by sharp spines, rather like the perky eyebrows I associate with clerics of a certain age. Under high magnification it would be apparent that the eyes are composed of many tiny lenses – they are what are known as compound eyes, similar to those of houseflies or bees. The whole animal is a dull pinkish-to greenish-grey colour, the kind of colour I used to get as a kid when I mixed all my powder paints together. The front of the head-shield is subtly bowed upwards about the middle. The tail (or telson) has a triangular cross section, and it makes a stoutly elegant termination to the animal. The middle part of the body is defined on its top surface as a kind of convex median lobe over about half its length: this is where the muscles that power the legs are lodged. The leading edge of the head-shield is thickened into a prominent marginal rim that is prolonged backwards into short spines; this part of the body needs to be strong to butt into the sands and mud that line the floor of Delaware Bay. On the shore there are several beached crabs lying on their backs, waving their legs at the sky. They bend almost double along their middle hinges, but their best efforts still fail to turn them over (it would be different under water). If they remained on their backs, greater black-backed gulls would soon come along to peck them to pieces. Before setting them aright, I have a chance to see how delicately each of the paired jointed limbs under the head-shield carries a set of pincers at its tip. I am reminded of the manual toolkit owned by the eponymous hero of the movie Edward Scissorhands. They are indeed picky little tools. Nearer the front end of the head-shield, where the carapace is doubled back from the top surface into a blunt point, a very delicate set of pincers at the centre of the animal and close to the mouth, looks just the thing to feed titbits towards the innards. The bases of the legs are really quite stout and equipped with blunt spines that face one another along the midline of the animal: they can be used like nutcrackers to crack shellfish if needs be. I begin to understand how these creatures can grab a living from the waters of Delaware Bay. Behind the legs are a few pairs of flattish flaps that cover up intricately folded book lungs. Like every marine animal the horseshoe crab needs to breathe dissolved oxygen, and as long as this breathing apparatus can be kept moist under its protective covers the crab can survive on land. Hence the female can endure her risky excursion to lay her eggs in the sand. The shore may be an unwelcoming nursery, but might still be preferable to a sea where every cubic metre holds a thousand twitching antennae sensing free food. It is time to turn our crab over to allow it to trundle away. It heaves itself along like a battered tank: slowly and undignified, as if to signal ‘I have survived endless battles, and survival is all’. As it performs its lurching exit to the sea, it leaves a track behind on the muddy sand surface. The paired imprints of the limbs are prominent; even the tips of the pincers leave their doubled marks. And the tail, dragged behind, leaves a groove between, as a child might scribe with a stick clumsily trailed across the strand.

      Horseshoe crabs are not really crabs at all; indeed, they are only very distantly related to crabs in so far as both kinds of animals propel themselves through the sea on spindly jointed legs. Animals with useful appendages of this articulated kind are known as arthropods (from the Greek: jointed legs). They are classified together in Phylum Arthropoda, a vast animal group that includes all the living insects, as well as spiders, millipedes, and a host of marine ‘bugs’ of all kinds. Crabs are crustaceans, along with lobsters, shrimps, and woodlice (pillbug to some). Horseshoe crabs are no more crustaceans than are butterflies. They do not have the flexible antennae or ‘feelers’ adapted to sensing the environment that are a common property of Crustacea and insects: these delicate organs both feel and touch, and smell. Instead, in the horseshoe crab the head appendages are modified at the front into a pair of useful pincers, or chelicerae, which I had observed in my stranded animal lying on its back. The significance of this apparently small feature will become apparent. The scientific name of the horseshoe crab is Limulus polyphemus (I shall need to use scientific names throughout this book). By day the beach throngs with feeding wading birds: thousands of them skitter nervously away from human intruders in animated, piping, fluttering waves, always beyond reach. Like most waders, many of them are dressed in shades of brown and grey, but the different statures of several species are obvious even to an inexperienced birdwatcher. СКАЧАТЬ