The detachment of barnacles (under shear and tensile loads) from silicone was investigated with the aid of high-speed digital video recording. A handheld probe was used to apply loads to the shells of barnacles attached to three clear siliconeelastomer coatings of known thickness applied to glass plates. The tests were performed in the laboratory in air and underwater. Representative data are presented as a qualitative description of separation at the barnacle adhesive-silicone interface. Detailed examination of adhesive separation during detachment provided new insight into the nature of a marine biological adhesive on a low modulus, artificial surface. The visible response of the barnacle adhesive on silicone under external shear and tensile loading was suggestive of the viscous fingering seen in Saffman-Taylor instabilities. Complex branching separation occurred in rapid progression, usually within 100 ms. The results suggest that the barnacle adhesive exhibits rheological responses of a viscous material at the interface with silicone surfaces. Additional experiments with time-lapse photography demonstrated that the adhesive was stable underwater but became dehydrated or coalesced when exposed directly to air. A simple model of the adhesive system of a barnacle in contact with silicone based upon Balanus eburneus is proposed to assist in the development of a more complete understanding of barnacle adhesion.