“You can only describe the tropical whip spider as evolution’s perfect design for an arthropod killing machine,” says Verner Bingman, a behavioral neuroscientist and National Geographic grantee.
While whip spiders are arachnids that fall under the arthropod phylum, they’re not actually spiders. Whip spiders have eight legs, but the front two have evolved into antenniform legs that extend up to two feet long. These legs wiggle around like whips to gather sensory information, earning whip spiders their name. The arachnids also have appendages called pedipalps, which Bingman describes as being like “pliers with sharp teeth.”
“They’re these kind-of serrated blades that the whip spiders use to clasp and crush its prey,” he says. “They have remarkable weaponry for killing.”
Despite his chilling description of this creature that looks like it just walked out of a nightmare, Bingman and his colleague Daniel Wiegmann, spend their nights catching whip spiders by hand because the scientists are so fascinated by the animal’s remarkable navigational abilities. At the La Suerte Biological Field Station in Costa Rica, the team placed radio transmitters on whip spiders and then moved the arachnids ten meters from their home tree to a location where they had never been before. The transmitters fell off the next time the whip spiders shed their exoskeletons but, before then, Bingman and Wiegmann came back and found that each whip spider had returned to almost exactly the same spot on the tree from which it had been removed.
The dense rainforest is a challenge for humans to navigate, let alone whip spiders. Verner explains, “I can’t impress upon you enough how nasty it is walking through this crap. It’s dark, the ground is uneven, you go up, you down, there are tree limbs. You’re tripping, you’re falling, it’s rainy, it’s muddy, there are puddles, there are obstacles everywhere. And these guys get back!”
This behavior is practically unknown in invertebrates. In fact, Bingman says the whip spiders’ abilities are much more reminiscent of the navigational skills found in homing pigeons and sea turtles, who are known for being able to find their way home across great distances, though perhaps dung beetles should be added to that list, given their star-gazing orientation skills.
“So the animals find their way home. What’s the big deal about that?” Bingman quips. Then he explains exactly what that big deal is: “When we observe animals doing remarkable things, our first reaction is ‘wow’ and we want to know more about it. Animal natural history has inspired human curiosity for as long as people have lived.”
With that sense of discovery motivating them, Bingman and Wiegmann set out to determine just how the whip spiders are able to make their impressive homecomings. Knowing that whip spiders already have poor eyesight, the team covered the animals’ antenniform legs with nail polish, temporarily blocking their senses of smell and touch, and displaced the arachnids again. This time the whip spiders were unable to find their way back home, demonstrating the arachnids’ dependence on smell and touch for navigation.
Still, whip spiders may not be quite up to the challenge of the thousand-mile journeys of homing pigeons or sea turtles. “The navigational ability of whip spiders manifests itself in a pretty small flippin’ brain, if the truth be told,” Bingman says. But “it’s really, really exciting to look at how a true kind of navigational system can evolve with the relatively simple nervous system that these guys have.”
Check out Bingman’s research about other animals on the move—migratory birds.