Killer Plants Routinely Outsmart Ants With Clever Trick

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A variety of pitcher plant cultivated in Hawaii. David Eickhoff [CC by 2.0]/Flickr

Plants may not have brains, but that doesn't mean they can't be smarter than organisms that do. For instance, a carnivorous pitcher plant from Borneo has been found to employ one of the cleverest tricks in the botanical world, routinely outsmarting unwitting ants, their favorite prey, reports Reuters.

Pitcher plants are insect-eating flora that have evolved modified leaves known as a pitfall traps, which form slippery cups filled with liquid that are designed to lure prey in, but not let them out. This Borneo variety has a special feature, however, capable of exploiting natural weather fluctuations to adjust the slipperiness of its pitfall traps in order to maximize the size of its meals.

The trick is in how the plant employs this ability to lure in gobs of ants. In hot, sunny weather, the plant's surface dries and loses its slipperiness, making it safe for ants to visit. Ants serving as scouts discover and collect sweet nectar from the trap, and return to their nest to lead even more ants back to the location of the food. As more ants arrive, and the day lengthens, the plant begins to secrete a sugary nectar. This, in turn, primes the trapping surface to become wet through condensation at lower humidity levels than other plant surfaces, making the surface slippery once again.

The plant is thus able to feast on far more ants than it would have otherwise if it didn't let the first ants escape. In the plant world, this trick might be as ingenious as it gets.

"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.

There are about 600 species of carnivorous plants in the world. Though pitcher plants are a common form, there are also some plants with sticky flypaper-like surfaces, and others which utilize snap traps (such as with the Venus flytrap), among other strategies. It is believed that these killer plants evolved to be carnivorous to compensate for nutrient-poor habitats. Though most are designed to trap insects, some are capable of trapping and consuming small mammals.

Interestingly, Bauer believes that although ants routinely get trapped and eaten by pitcher plants, the ants are not necessarily getting a raw deal. He proposes that a system of mutual benefit may be at play.

"What superficially looks like an arms race between nectar robbers and deadly predators could in fact be a sophisticated case of mutual benefit," Bauer explained. "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."