  Crayfish are nocturnal animals that mainly rely on their chemoreceptors to
locate food. On a crayfish scale chemical stimuli received from a distant
source are dispersed by an ambient flow rather than molecular diffusion. When
the flow is weak or absent, food search can be facilitated by currents
generated by the animal itself. Crayfish employ their anterior fan organs to
produce a variety of flow patterns. Here we study the flow generated by
Procambarus clarkii in response to odour stimulation. We found that while
searching for food the crayfish generates one or two outward jets. These jets
create an inflow which draws odour to the crayfish's anterior chemoreceptors.
We quantified velocity fields in the inflow region using Particle Image
Velocimetry. The results show that the inflow velocity decreases proportionally
to the inverse distance from the animal so that it takes about a minute for an
odour plume to reach the animal's chemoreceptors from a distance of 10 cm. We
compare the inflow generated by live crayfish with that produced by a mimicking
device, a phantom. The phantom consisted of two nozzles and an inlet providing
two jets and a sink so that the overall mass flux was zero. The use of a
phantom enabled us to analyze the inflow at various jet parameters. We showed
that variation of the jets' directions and relative intensities allows changing
the direction of odour attraction. These results provide a rationale for
biomimetic robot design. We discuss sensitivity and efficiency of such a robot.
