Daily Archives: 13th of January 2011

Life in a place of death? Pitcher plants as habitat

It shouldn’t be a surprise that there are things living in guts. Whenever I turn on ITV there’s an advert for yoghurt with Yummy Tummy Bacteria. Apart from microbes, there can be relatively complex invertebrates like worms. But you might not expect so much to be living the trap of a pitcher plant. Microbes maybe, but invertebrates? Didn’t these traps evolve to eat invertebrates? A forthcoming review for Annals of Botany, Traps of carnivorous pitcher plants as a habitat: composition of the fluid, biodiversity and mutualistic activities by Wolfram Adlassnig, Marianne Peroutka and Thomas Lendl shows it’s a lot more complex than that. The traps might digest prey, but they’re also home to small ecosystems. The creatures within include a microscopic zoo, but also larger animals like crabs, spiders and frogs.

How pitchers work

Diagram for a Pitcher Plant

Diagram for a Pitcher Plant by Adlassnig et al.

They start with an explanation of how pitcher plants work. They’re not as dynamic as some other carnivorous plants like Venus Fly Traps. At the top A there’s the hood with glands that produce nectar to entice prey in. However when they land on the rim B insects find the surface is slippy. Make a mistake and you’ll fall slightly down the trap. It then the insect discovers the rim is covered with inward pointing hairs, making it very difficult to climb up. Struggling here is likely make you slip into region C.

This zone is all about getting the prey down further. The hairs make it impossible to climb up and some pitchers also have loose wax crystals. The area labelled D is the bottom of the pitcher. This part of the plant exudes digestive enzymes that pool at the bottom of the pitcher E. Here insects drown.

You wouldn’t expect some of them to drown. Adlassnig et al. point out that some ants can run along the surface of pure water due to surface tension. They can’t in the pools of many pitchers. The reason is that the pools contain surfactants. Around the house you’d find them in things like soap and detergent. In the plant their role is to reduce the surface tension of the liquid allowing the prey to fall in and drown.

If pitchers are so bad, why so insects enter? Aside from the nectar glands in A and sometimes B, there’s another factor. It turns out these fluids might also have a narcotic effect, and the odour attracts insects to the plant where on the outside, F, they find a nice rough surface for any insect that wants to climb up and investigate. But it’s not just food that enters the pitcher.
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