Great Whip Spider Boom: Are These Exotic Arachnids a Spider or Tailless Scorpions?

Tailless whip scorpions are neither spiders nor scorpions. They belong to an arachnid order called Amblypygi, which means "blunt rump" because they have no tails.

The current surge of behavioral and neurophysiological studies about whip spiders has opened a doorway into their strange sensory world. Researchers have observed that more than 150 species participate in intriguing activities, including homing, territorial defense, cannibalism, and tender social relations.

Whip Spiders Has Eight Legs But Only Walks On Six

Whiplash-wielding spiders have eight legs. They only walk on six. Antenniform legs are sensory structures on the front two legs. Three to four times longer than the walking legs, these legs have hair-like sensory structures. Their relentless action sweeps everything, earning them the name "whip spiders." Whip spiders use their antenniform legs like a blind person would a cane, only they can also smell, taste, and hear with them.

Whip spiders' lives revolve around using their legs for hunting --a fact that gives these arachnids a hazardous predator presence throughout the world's tropical and subtropical environments. When Nebraska-Lincoln biologist Eileen Hebets studied the hunting behavior of whip spider Phrynus marginemaculatus, she discovered a well-choreographed pattern. The whip spider shot an antenniform leg at the prey. Then, the antennae ended with leg-like structures. Finally, it whipped out its antennae-laden pedipalps and slammed them down on the ground.

"The way they move their legs is so graceful," Hebets told The Scientist. "Their movements seem intelligent. And they have this incredible repertoire of sensory capabilities along with interesting behaviors."

Sparring is one of those habits. They fight by vibrating their antenniform legs at each other. At first, it was considered that the opponents touched each other. Using high-speed video, Hebets proved that the antenniform legs never connect. The whip spiders' legs are held close to their opponents' knees, with long, thin sensory hairs in a socketed base.

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Whip Spiders Can Detect Losing Opponent

Electrophysiological research found that these hairs are near-field sound sensors that detect the opposing leg-waving wind. After Hebets trimmed off the sensory hairs, contest-winning antenniform leg waving no longer predicted duration. Researchers uploaded their study, titled "Evidence for Air Movement Signals in the Agonistic Behaviour of a Nocturnal Arachnid (Order Amblypygi)," on Plos One.

Antenniform legs have sensory hairs on them that detect airborne scents. Whip spiders utilize their sense of smell to locate their way home. Along Bowling Green State University scientists Verner Bingman and Daniel Wiegmann, Hebets collected whip spiders in Costa Rica. The researchers covered the eyes of some of them by painting their nails black.

For other arachnids, input from the tips of the antenniform legs was blocked by either nail polish or scissors. They fitted microscopic radio transmitters to the animals' backs and then released the experimental groups ten meters from their homes. The whip spiders could generally get back without using their eyes.

However, "Importance of the Antenniform Legs, but Not Vision, for Homing By the Neotropical Whip Spider Paraphrynus Laevifrons" claims that whip spiders with aberrant antenniform leg tips completely lost their homing capacity.

Whip spiders and their comrades also hurry home to avoid any predators. Up to 20 percent of laboratory interactions conclude with one opponent swallowing the other.

Researcher Kenneth Chapin also discovered that the Puerto Rican species Phrynus longipes is extremely territorial. The only way to ward off the whip spiders is to "do what a wolf pack or a house cat would do."

Whip Spider Lives Solitarily Despite Having Violent Lives

Whip spider studies show that the whip spiders lead solitary, violent lives. Some study, however, depicts these formidable carnivores as loving lovers. The whip spider courtship ritual can run for eight hours and includes plenty of antenniform leg rubbing.

Linda Rayor, an entomologist at Cornell University, has demonstrated that some animals have remarkably sociable parent-offspring associations. Rayor bought multiple kinds after seeing a whip spider in Costa Rica. One day, Rayor witnessed a mother sitting amidst the "whipping-cracking" of her kids. The group worked in their delicate antenniform legs. That was the only time that they ever witnessed arachnids demonstrate goodwill.

Rayor's study, "Social Behavior in Amblypygids, and a Reassessment of Arachnid Social Patterns," reveals that moms and siblings usually form small groups before young individuals achieve sexual maturity. Thus, they generally sit in range of one another to keep continual contact.

Despite all the recent investigations, very little is known about whip spiders' brains. The mushroom body is especially big and twisted in whip spiders. In insects and other invertebrates, the mushroom bodies are associated with information processing, learning, and memory. Whip spiders have the largest mushroom bodies, for their size, of any arthropod. But what these structures function in whip spiders and how sensory input from the antenniform legs is implicated remain unclear.