Date of Award

Spring 2006

Document Type

Restricted Thesis

Terms of Use

© 2006 John C. Tuthill. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts



First Advisor

Rachel Merz


Many animals can discriminate between two visual stimuli based solely on differences in the orientation of polarized light. The known functions of polarization sensitivity include orientation, navigation, inter-specific communication, camouflage-breaking, and contrast enhancement. I tested the hypothesis that polarization sensitivity enhances the detection of a moving, transparent object by examining the escape response of the red swamp crayfish (Procambarus clarkii) from a visual threat. A transparent, birefringent target trans-illuminated by either partially linear polarized or unpolarized light was advanced toward individual crayfish. The optical axis of the target was aligned such that it would be conspicuous to a viewer with polarization sensitivity when trans-illuminated by polarized light. Under polarized light, significantly more crayfish retreated from the target than under unpolarized light of identical intensity (pP. clarkii and the signal crayfish Pasifastacus leniusculus, these results provide the first behavioral evidence for polarization sensitivity among crayfish. The ecological function of this ability is unclear, but may enhance the detection of fish with mirror-like scales, transparent zooplankton, or macroinvertebrates. Because escape responses are generally more reliably induced than other behaviors, the method employed in this study may prove useful for examining sensory capabilities in other species.


Portions of this thesis previously published in Tuthill, J.C. and Johnsen, S. (2006). Polarization sensitivity in the red swamp crayfish Procambarus clarkii enhances the detection of a moving transparent object. J Exp Biol 209, 1612-16.