| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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WILD LIVES Scorpion: A Case Of Arrested Development
If scorpions had a motto, it would be “if it ain’t broke, don’t fix it.” These heavily armored creatures have barely changed their design since they first left the water for the land. That was some 420 million years ago, when armored fish whose jaws could crush less well-protected creatures prowled the seas. Like many large animals of the time, scorpions traded flexibility and speed for the security of chain mail. But their move to land was likely what saved them. Had they remained in the water, scorpions might have followed their ancestors, the sea scorpions, and armored fish into extinction, as naked but fast and furious newcomers came to rule the oceans. The scorpion’s ancient heritage remains evident in many of its traits. They are archaic-looking beasts, with a menacing aura projected by a wickedly curved, barb-tipped tail, sharp-clawed pincers held out stiffly like a bodybuilder’s arms, and the lack of any discernible face. The tail itself is ridged and keeled, one segment linked to the next like pop beads, and the whole thing ending in a bulb and stinger. Scorpions are most feared for their dangerous tails and those with the thickest tails—and larger poison glands—pack a nasty wallop. But poison is costly to manufacture, so many species rely more on their heavy pincers to wrestle their prey into submission. Trackways found in the Tumblagooda Sandstone of Western Australia show that early scorpions in the Silurian Period were over three feet long—a third larger than the biggest lobster ever caught. But, as is usual with creatures that leave the water for the land, scorpions have shrunk over the eons. Today’s whoppers are the southern African Hadogenes troglodytes at eight inches long, and Pandinus imperator of tropical Africa, which weighs well over an ounce. Pregnant females can be almost double that weight. In contrast, little Microtityus waeringi from Brazil has to really stretch to make not quite half an inch from the front of its head to the tip of its tail. The doubtful distinction of “Most Deadly Scorpion” goes to species of the Centruroides genus, which kill several hundred people each year in Mexico. Scorpions have a very slow metabolic rate so they can go up to a year without eating or drinking. They get all the moisture they need from their prey and recycle it so efficiently that none is lost through excretion. Scorpion poop looks very much like chalk powder. Watching them move brings to mind a remote-controlled toy tank. As they lurch along on absurdly skinny legs, you half expect to hear wheeps, whirrs and clanks. A rock in the path brings them to an abrupt halt, and you can imagine a joystick somewhere going “Up now” or “Turn sharp right.” For some reason, they always seem to move in straight lines with right-angled turns, whether in forward or reverse. Most scorpions are ambush predators, lying in wait until prey comes within strike distance. Some are much more active hunters. But all, when hungry, go on the prowl, though they never seem to have any kind of plan. In fact, they seem to zip along with no apparent reason. Scorpion expert Eric Volschenk, of the American Museum of Natural History, describes their technique as “All systems go. They hold out their pincers and rush forward until they hit something they can eat.” I once tried to keep scorpions as pets. Mine holed up all day and most of every night, crouching motionless under a chunk of bark or slab of rock, the tips of their pincers barely showing. Occasionally they would emerge from their shelters at night and hunt, decimating the crickets I had tossed into their terraria. It’s important not to overfeed captive scorpions; one of my females became so fat that she literally started to split. Her black armor plates pushed apart, revealing the bright white membranes beneath. She eventually gave birth to live young after an incredibly long gestation period of about 18 months—much the same as that of the elephant. Hunting scorpions aren’t helped much by their eyes, which are sensitive to movement and light, but do not form the clear image that bifocal primates are accustomed to. A scorpion can have anywhere from six to twelve eyes, depending on the species, with the two largest in the center of the carapace, flanked by tinier ones on each side. Wave a hand, or a stick, at a scorpion, and it will strike, probably as the separate images formed by its eyes intersect at just the right distance. These clunky predators do have chemo-sensory receptors, concentrated on the comb-like structures called pectines between the last pair of walking legs. Pectines seem to be used mostly to sense ground textures and to pick up scents such as mating pheromones. One might say that a scorpion’s “nose” is at the level where its navel would be if it had one. Scorpions may also have a second sniffer system near their stingers capable of detecting scent molecules carried in air. Like many long-time survivors, scorpions are generalists when it comes to food. These carnivores are notorious for eating almost anything that comes their way alive, including other scorpions. In fact, cannibalism seems to be critical to the survival of some California sand dune scorpions. But all scorpions will happily eat cockroaches, crickets, beetles, spiders, centipedes, and millipedes. Larger scorpions will even tackle on creatures as large as baby mice and birds. Most arachnids, such as spiders and ticks, can only eat liquid foods. But scorpions are messier feeders than their kin. Unlike spiders, scorpions don’t inject tissue-dissolving chemicals into prey. They literally shred prey with powerful jaw-like chelicerae, macerate the flesh with digestive juices, and suck out the liquids, discarding any insoluble parts. It’s rather like chewing a wad of gum, though much more nutritious. On a recent trip to Burma, Academy photographer Dong Lin set up an interspecies gladiator combat when he placed an eight-inch snake near a four-inch scorpion. The scorpion seized the snake, stung it repeatedly, and then fed its writhing length into remorselessly chomping jaws. It reduced the snake to a pasty, whitish pellet containing minerals from the snake’s bones and a few intact scales. Even the snake’s skull was gone. The same characteristics that served ancient marine scorpions well have allowed their terrestrial descendants to infiltrate nearly every type of land habitat. The thick, wax-coated cuticle that kept brine out now helps keep body fluids in. Even in the driest deserts, scorpions are independent of surface water, getting all they need from their prey. Ice doesn’t worry them at all. Scorpions can be frozen into solid chunks of ice over winter and still go about their business, completely unperturbed, come spring. At the same time, they seem to have retained their ability to survive in water. Their four pairs of booklungs, breathing organs that resemble neatly stacked book pages, have covers that snap into place like the hatches of a submarine, allowing scorpions to remain submerged for many hours without any danger of drowning. This primitive survival gear has helped scorpions to survive the rise of vertebrates, the fall of the dinosaurs, and the advent of mammals. But scorpions don’t have things all their own way. Thick armor plating makes them slow and clumsy, and there is a noticeable lag between a stimulus and their response. Faster, nimbler animals find scorpions easy prey. To capture a scorpion, you need only place a large jar behind it, and then menace it with the lid. With its pincers waving threateningly and its tail promising instant retaliation, the hapless beast will always reverse course into the jar. In many parts of the world, scorpions are regarded as a delicacy. Restaurants in Thailand serve platters of cooked scorpions, arranged like so many small lobsters, with bowls of savory dipping sauces. Another primate, baboons, makes quite a good living from scorpions. A troop moving through an area will methodically flip large rocks, strip loose bark from trees, and roll over logs. When a baboon discovers a scorpion, it makes a quick snatch, snaps off the poison bulb at the end of the tail, and crunches up the newly defenseless animal as a tasty snack. In California, scorpions are a staple food for all kinds of animals, including rodents, kit foxes, pallid bats, elf owls, and even ringtailed cats. The late Arizona State University scorpion biologist Herbert L. Stahnke discovered the ringtail’s partiality while keeping live scorpion specimens in his laboratory. One day, the animals started to disappear from their lidless glass tanks, sometimes just one, sometimes two or three at a time. The only clue to their fate was a trail of broken-off tails. Finally, the irate Stahnke decided to sit in his darkened laboratory and wait for the mystery killer. He saw a ringtailed cat insinuate itself through a barely-opened window, stroll over to a tank, nip off a scorpion’s tail, and then dine leisurely on the disarmed creature. Stahnke at once took steps to convert this private pantry back into a research laboratory. Given their long history, scorpions are likely to survive far into the future. They may be primitive and lacking in brainpower, but their armor and slow metabolism, as well as their habit of living under rocks, in burrows and other sheltered areas, may well protect them from radioactive fallout in the event of a nuclear attack. Scorpions have survived numerous meteor impacts and successive glaciations. They aren’t fussy, so they’re not likely to ever run out of food, and their venom is effective against many other animals—including other species of scorpion. They could probably just cover their book lungs and hunker down until all the noxious chemicals had passed, emerging to feed off other survivors. Suzanne Ubick is Assistant Editor of California Wild. |
