by Joseph DeSisto
Thought we were done with whip-spiders? Never! Well at least not yet, because I just came across this little gem of a paper: “Fishing Behavior in a Giant Whip Spider” by Ladle and Velander (2004). With a title like that, I had to read on.
High in the mountains of Tobago, an island off the coast of Venezuela, tropical rainforest is pierced by cool streams, twisting and turning between dripping-wet boulders. By day, freshwater crabs scour the rock surfaces, emerging from the water to feed on algae and detritus. Far enough upstream to avoid predatory fish, the crabs flourish, along with prawns that swarm the fast-flowing water.
As night falls, the crabs continue to feed, but from the dark and hidden places emerge larger, more fearsome beasts: whip-spiders of the species Heterophrynus cheiracanthus. Heterophrynus whip-spiders are common in South American rainforests, and this species is one of the biggest. With a body length nearly 1.5 inches and a leg span many times that, cheiracanthus is not an arachnid to mess around with.
As a whip-spider traverses the algae-covered boulder, crabs move out of its way, although they are not the targets of this night-time hunt. Using its whip-like front legs, cheiracanthus feels its way through the mist, finally reaching the water’s edge. Here it raises its pedipalps, and waits.
The whip-spider is patient. It holds its grotesquely spiked pedipalps, several times longer than its own body, perfectly still, while the whip-like legs dip into the water, feeling for the slightest movement. On a productive night, the stream is swarming with prawns, and one of these will inevitably be unlucky enough to swim too close to the boulder. When it does … Wham!
Pedipalps snap shut like mouse traps, only these traps are lined with long spikes that impale the prawn — death is quick. As soon as the crustacean stops twitching, the whip-spider retires to its crevice, past wary crabs, and digs in.
Whip-spiders are skilled hunters, and have been observed eating all sorts of invertebrates. There is even a report of one eating a small lizard (Kok 1998). But Ladle and Velander’s paper is, as far as I know, the only record of a whip-spider actively hunting aquatic prey. What’s more, H. cheiracanthus is one of only two arachnids known to eat prawns — the other is a fishing spider, which is basically cheating (Van Berkum 1982). My only complaint is that there are no pictures, so if you are planning a tropical getaway to Tobago, forget relaxing on the beach. There are fishing whip-spiders just upstream.
Kok, P. 1998. Anolis nitens chrysopepsis (golden-scale anole) predation. Herpetological Review 291: 41.
Ladle, R.J. and K. Velander. 2003. Fishing behavior in a giant whip spider. Journal of Arachnology 31(1): 154-156.
Van Berkum, F.H. 1982. Natural history of a tropical, shrimp-eating spider (Pisauridae). Journal of Arachnology 10: 117-121.