Finding the source of a pheromone plume in a turbulent flow is a greater challenge than finding an animal producing sound or visual signals. Nonetheless, animals responding to pheromones offer some of the most spectacular examples of remote responses to stimuli. These include male moths attracted to females over hundreds of meters and perhaps even farther. Over evolutionary time, receiving organisms have been selected to search efficiently and to find a source as quickly as possible: many odor sources (whether food or mates) do not last long – the odor source moves or another animal will get there first (Cardé & Willis 2008).

Searching animals exploit the invisible odor “landscape” created by high and low concentrations of countless molecules in overlapping plumes released by other organisms (Atema 2012; Hay 2009; Nevitt 2008). These chemical plumes occur in a wide range of spatial scales and durations. For example, in the sea, they range from the pheromone plume released by a single planktonic copepod, a few millimeters long, to the dimethyl sulfide odor plumes from a plankton “hotspot,” kilometers wide. Odor signals have a significant but limited life before the molecules are dispersed or broken down.