Visual control of refuge recognition in the whip spider Phrynus marginemaculatus.

Amblypygids, or whip spiders, are nocturnally active arachnids which live in structurally complex environments. Whip spiders are excellent navigators that can re-locate a home refuge without relying on visual input. Therefore, an open question is whether visual input can control any aspect of whip spider spatial behavior. In the current study, Phrynus marginemaculatus were trained to locate an escape refuge by discriminating between differently oriented black and white stripes placed either on the walls of a testing arena (frontal discrimination) or on the ceiling of the same testing arena (overhead discrimination). Regardless of the placement of the visual stimuli, the whip spiders were successful in learning the location of the escape refuge. In a follow-up study of the overhead discrimination, occluding the median eyes was found to disrupt the ability of the whip spiders to locate the shelter. The data support the conclusion that whip spiders can rely on vision to learn and recognize an escape shelter. We suggest that visual inputs to the brain's mushroom bodies enable this ability.

Vertical-surface navigation in the Neotropical whip spider Paraphrynus laevifrons (Arachnida: Amblypygi).

Studies on whip spider navigation have focused on their ability to locate goal locations in the horizontal plane (e.g., when moving along the ground). However, many species of tropical whip spiders reside and move along surfaces in the vertical plane (e.g., trees). Under controlled laboratory conditions, the current study investigated the ability of the tropical whip spider, Paraphrynus laevifrons, to return to a home shelter on a vertical surface in the presence of numerous, similar and competing refuge sites, as well as the distribution of navigational errors in the vertical, horizontal and diagonal plane. We also assessed the relative importance of sensory cues originating from a previously occupied home shelter compared to the position of a previously occupied shelter in guiding shelter choice. It was found that P. laevifrons displays robust fidelity in re-locating a home shelter on a vertical surface. When navigational errors did occur, they were not significantly different in all three directions. Additionally, cue-conflict test trials revealed that cues associated with an original home shelter, likely self-deposited chemical signals, were more important than sources of positional information in guiding the shelter choice of P. laevifrons.