Meeting Abstract

106.3  Saturday, Jan. 7  Why snakes flick their tongues: a fluid dynamics approach RYERSON, WG*; SCHWENK, K; University of Connecticut

The forked tongue of snakes is used to collect chemical molecules (odorants) from the
environment and deliver them to the vomeronasal organs in the roof of the mouth. Snakes
use two methods to sample odor molecules: a substrate touch with the tongue tips and
oscillatory tongue-flicking in the air. Among fork-tongued squamates, snakes are the only
group to employ oscillatory tongue-flicking for chemoreception. We used particle image
velocimetry (PIV) to examine the flow of air around the tips of the tongue during tongue-
flicking. This revealed that oscillatory tongue-flicks generate two pairs of counter-rotating
vortices that are maintained by the movement of the tongue tips. The tongue tips skim
along the margins of these vortices moving against their flow during both the upstroke
and the down stroke. In addition, the vortices draw fresh air (and chemicals) into the
path of the tongue, also in a countercurrent direction. This flow pattern maximizes the
encounter rate of the tongue with odorant molecules and because the tongue tips are
coated with mucous fluid, it greatly increases the rate of diffusion/sorption of odorants
into the fluid by thinning the boundary layer and maintaining a concentration gradient. The
pattern of vortex formation is dependent on the number of oscillations, size, and velocity
of the tongue, which vary greatly among species. We suggest that changes in these factors
maintain tongue movement within a specific Reynolds number regime that maximizes the
rate of odorant uptake.