Whip spiders, or amblypigids, are not spiders at all. They are arachnid cousins to scorpions and spiders, and are known for their long furry whip. "The whips are central to amblypigids' entire existence," says Linda Rayor, a researcher at Cornell University in New York. Amblypigids use their whips to assess the environment and lure prey straight into their jaws.

Amblypigids have a reputation for ferociousness. But, Rayor found that these arachnids may have been misjudged. In a study published in the Journal of Arachnology, Rayor revealed that amblypigids also use their terrifying-looking whips to do nice. In captivity at least, a mamma amblypigid approaches her spiderlings and brushes them with her whip, in what appears to be a friendly gesture. The spiderlings gently whip her too--brushing her palps and body.

The siblings also are friendly with each other: they stay only a whip length apart until sexual maturity (13 months) and in some species, even longer. The brotherly love has Rayor and her colleagues wondering: why? "Sociality is incredibly rare in the arachnids. Virtually all the arachnids are predators. It's very clear that there is a steep barrier to becoming social in these animals," Rayor says.

What is driving this behavior in amblypigids? Rayor thought it might be a microclimate preference: perhaps the siblings wanted to be in the same spot in the cage because of ideal humidity or temperature. Her experiments, however, showed this wasn't the case--they happily moved around to many types of microclimates. The priority was staying together.

Another hypothesis is that grouping might protect them against predation. But, amblypigids don't seem to have many predators in the wild. There are few documented instances of anything eating an amblypigid. Rayor says: "I suspect it is some kind of anti-predator response, but to be honest, I don't know."

-Flora Lichtman

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