Carnivorous Plants Use Pitchers Of "Slimy Saliva" To Catch Their Prey

Carnivorous plants supplement the meager diet available from the
nutrient-poor soils in which they grow by trapping and digesting insects
and other
small arthropods. Pitcher plants of the genus Nepenthes were thought to
capture their prey with a simple passive trap but in a paper in this week's
PLoS ONE, Laurence Gaume and Yoel Forterre, a biologist and a physicist
from the CNRS, working respectively in the University of Montpellier and
the
University of Marseille, France show that they employ slimy secretions to
doom their victims. They show that the fluid contained inside the plants'
pitchers has the perfect viscoelastic properties to prevent the escape of
any small creatures that come into contact with it even when diluted by
the
heavy rainfall of the forest of Borneo in which they live.



Since Charles Darwin's time, the mechanism of insect-trapping by Nepenthes
pitcher plants from the Asian tropics has intrigued scientists but is
still incompletely understood. The slippery inner surfaces of their
pitchers have - until now - been considered the key trapping devices,
while it
was assumed that the fluid secretions were only concerned with digestion.
Gaume and Forterre were able to combine their separate expertise in
biology
and physics to show that the digestive fluid of Nepenthes rafflesiana
actually plays a crucial role in prey capture.



The pair took high-speed videos of flies and ants attempting to move
through plants' fluid. Flies quickly became completely coated in the fluid
and
unable to move even when diluted more than 90% with water. Physical
measurements on the fluid showed that this was because this complex fluid
generates viscoelastic filaments with high retentive forces that give no
chance of escape to any insect that has fallen into it and that is
struggling
in it. That the viscoelastic properties of the fluid remain strong even
when highly diluted is of great adaptive significance for these tropical
plants which are often subjected to heavy rainfalls.



For insects, this fluid acts like quicksand: the quicker they move, the
more trapped they become. Its constituency is closely akin to mucus or
saliva,
which, in some reptiles and amphibians, serves a very similar purpose. The
exact makeup of this fluid, apparently unique in the plant kingdom,
remains
to be determined; however, it may point the way to novel, environmentally
friendly approaches to pest control.




Citation: Gaume L, Forterre Y (2007) A Viscoelastic Deadly Fluid in
Carnivorous Pitcher Plants. PLoS ONE 2(11): e1185.

doi:10.1371/journal.pone.0001185

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