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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

At night in the rainforest: Whip spiders, Amblypygi


Greatly elongated front legs enable the whip spider to sense food, mates, and danger.


In weeks past we visited cold hardy larvae of lacewings and dusty-wings as they searched for prey on trees and shrubs in chilly winter landscapes in Maryland. This week we hop on a jet and head roughly 1,800 nautical miles to meet some fearsome predators in the rainforests of Costa Rica. To witness their grim mien, one must don a headlamp, grab a flashlight, and plunge into the rainforest, best with a trusty guide.  Here members of the arachnid clan known as whip spiders, a.k.a tail-less whip scorpions or amblypygids, hunt for food. Unlike their distant relatives in Maryland that hunt by day, these denizens of the dark are often found underground in caves or deep in the tropical forest were they hide in hollows beneath rocks and in soil, or in tree holes by day. By night they hunt and ambush prey.


A nighttime walk along a rainforest trail is full of spooky encounters, including ones with amblypygids.  

While other arachnids such as spiders and true scorpions amble about on four pairs of legs, whip spiders use just three pairs for nocturnal strolls. The fourth pair of legs, found at the front of the creature, is extraordinarily long and thin and loaded with sensory structures to detect odors and objects including mates, offspring, and prey. These so called “whips” can be three to six times the length of the body and give the whip spider its common name. Whips can be moved in almost a complete circle around the creature and are very useful for detecting objects ahead, behind, above, and to the sides in a world of darkness.  

Once these spines get you, there is no escape.

Just in front of the whip-like legs is a pair of scary hinged appendages known as pedipalps.  This “sit and wait” predator uses its pedipalps to capture prey in much the same fashion as a mantid uses its spiny forelegs to grab its victims. As a tasty morsel enters range, a rapid strike of the pedipalps ensnares the prey in comb-like teeth. Usual meals include crickets, cockroaches, spiders and moths, but small lizards and even fish are known to be eaten by these clever predators. Once captured the victim is pulverized by two grinding jaws called chelicerae. Digestive enzymes are added to the pulpy mass and the whip spider ingests the liquefied meal.

As frightening as whip spiders appear, they are truly harmless to humans. In fact, some species have several admirable and somewhat endearing behaviors. One such behavior is a fine sense of direction. While wandering about the rainforest at night it is easy to get lost. On more than one occasion hapless adventurers have disappeared into a ravine while searching for a trail in dense tropical vegetation. Not so the whip spider! Research has shown that some whip spiders can find their way home after being moved more than 30 feet away from their refuge, all this without Google maps.


Watch as the whip spider senses the approaching danger of a giant finger and jets out of harm’s way. At one tenth of normal speed, see how the whip-leg of the arachnid reaches back to examine the intruder before turning on the speed.

For any mothers who might be reading this episode, think about the calories you burned lugging youngsters about when they wanted to be picked-up. Whip spiders lay from 10 to 90 eggs at a time. Mother whip spiders typically carry their young on their backs for several weeks after offspring hatch from eggs. In captivity, females of the Floridian whip spider, Phrynus marginemaculatus, continue to interact with their offspring for several months after the babes have departed from their mother’s back. Mothers were observed to move between small clusters of young ones. Females and offspring frequently engaged in gentle mutual stroking with their whip-like legs. How often these fascinating behaviors happen in the wild remains to be seen. The message conveyed by the mutual stroking is known only to the whip spider and her young, but on a dark night in the Costa Rican rainforest a gentle touch from mom could be a comforting signal, even to a whip spider.       


Bug of the Week gives special thanks to Carlos and the other nocturnal adventurers at Aguila de Osa who were the inspiration for this episode. Kenneth J. Chapin and Eileen A. Hebets treatise, “The behavioral ecology of amblypygids”, and the wonderful article “Social behavior in Amblypygids, and a reassessment of arachnid social patterns” by Linda Rayor and Lisa Anne Taylor, were used as references for this episode.