Fig. 3. Tritonia diomedea often detect and locate upstream conspecific odour sources in the flow tank. T. diomedea tracks with (solid lines) and without (dotted lines) conspecifics in an upstream odour stimulus chamber (one slug in osc, two slugs in osc*). With upstream conspecifics, 12 of 20 slugs crawled upstream to make direct contact with the upstream grille and seven found the osc (x marks point of first contact with upstream grille). Only two slugs in controls crawled upstream to make contact with the upstream grille without first contacting the side walls of the tank, and none found the empty osc (o marks point of first contact with upstream grille). Tracks are projected onto a scaled and simplified flow tank diagram. Flow tank width, 1 m. See Fig. 3 movie in supplementary material for an example movie.