For tests with prey and conspecifics, distance from the upstream odour stimulus chamber (averaged over the entire trial) was compared to controls without odour stimuli (paired t-test, d.f.= number of pairs—1).

Distance values are means ± s.e.m.

For both prey and conspecific odours, slugs in experimental trials were, on average, significantly closer to the odour source. For tests with predators,the change in distance from the odour stimulus chamber was calculated while the slugs were in a section of the flow tank downstream of the chamber. Paired data were limited to six slugs that crawled into this section of the tank during both trials, and thus we also tested for differences without pairing. Only the latter test is significant, and we therefore suggest there is moderate evidence that T. diomedea moves downstream away from predators in this experiment.