Whip spiders (Amblypygi) are a small and understudied group of arachnids characterized by long antenniform legs and raptorial pedipalps. Due to their nocturnal habits, secretive nature and geographical distribution there have been very few studies of feeding behavior in this group. Here, we report a remarkable foraging strategy adopted by the giant tropical whip spider Heterophrynus cheiracanthus (Gervais 1844) inhabiting rocky outcrops adjacent to mountain streams running through primary tropical rainforest on the Caribbean island of Tobago. Heterophrynus cheiracanthus positions itself close to the stream edge on a vertical rock surface with pedipalps fully extended and antenniform legs frequently entering the shallow water. Freshwater prawns of the genus Macrobrachium are caught while still submerged in the water despite the whip scorpion being unable to use the trichobothria on the walking legs. Possible mechanisms of prey detection are discussed.