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 Scientists say the tropical carnivorous plant regularly exploits
natural weather fluctuations to adjust the slipperiness of its
pitfall traps in order to capture and dine on batches of ants at a
time rather than individual ants.
The research involved an Asian species of pitcher plant, so named
because its leaves form cup-shaped insect traps that look like a
pitcher.
When the rim of the plant becomes wet, it gets extremely slippery
and ants walking on the surface fall victim to the voracious
vegetation.
In hot, sunny weather, however, the surface dries and becomes safe
for ants to visit. Individual ants serving as scouts for their
colonies discover and collect sweet nectar from the trap and return
to their nest to tell their fellow ants where to find a nice meal.
 Numerous ants then march unwittingly into the trap in search of food
and are captured because the plant has made its trap slippery and
inescapable. So by letting the individual scouts escape, the plant
eventually manages to capture much more prey.
To control when its trap is slippery, the pitcher plant secretes
sugary nectar that primes the trapping surface to become wet through
condensation at lower humidity levels than other plant surfaces.
That activates the trap during afternoons when many day-active
insects are still out and about.
"Of course a plant is not clever in the human sense - it cannot
plot. However, natural selection is very relentless and will only
reward the most successful strategies," said biologist Ulrike Bauer
of Britain's University of Bristol, who led the study being
published on Wednesday in the scientific journal Proceedings of the
Royal Society B.
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There are about 600 species of carnivorous plants known worldwide.
The pitcher plants generally grow in nutrient-poor habitats, which
is why they capture animal prey to feed on. Most species trap
insects. A few attract small mammals and collect their feces for
nourishment.
"What superficially looks like an arms race between nectar robbers
and deadly predators could in fact be a sophisticated case of mutual
benefit," Bauer said.
"As long as the energy gain (eating the nectar) outweighs the loss
of worker ants, the ant colony benefits from the relationship just
as much as the plant does."
(Reporting by Will Dunham; Editing by Peter Cooney)
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