The internal walls of pitcher plants prevent insects from escaping by clogging their feet with a flaky, waxy substance and being rough.

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“The plant lures animals, from insects to amphibians to rats and even birds, into a modified leaf that forms a bowl. It does this by a combination of color, nectar, and scent." (Zygote Quarterly)

Learn more about the pitcher plant's strategy in Tom McKeag's case study, "Return of the Swamp Thing" on page 16 of Zygote Quarterly:
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"The most elaborate of all these leaves turned into pit-fall traps are developed by the plants that are known, simply and without qualification, as pitcher plants…Their trapping strategy is the same as the trumpet pitchers. They entice insects with fragrant nectar. The walls of their traps are made even more treacherous by a flaky waxy surface that peels off and clogs the feet of insects so that they lose all chance of adhesion. As their victims tumble into the water and start to struggle to save themselves, the disturbance stimulates glands in the pitcher walls which start to discharge a digestive acid. This is so powerful that a fly will be reduced to a hollow shell within days and a midge will disappear entirely within hours. The whole device is so effective that these pitchers can trap not just small insects, but cockroaches, centipedes and scorpions. The rajah is said to be able to consume mice." (Attenborough 1995:77-78)

"[Abstract] Pitcher plants of the genus Nepenthes efficiently trap and retain insect prey in highly specialized leaves. Besides a slippery peristome which inhibits adhesion of insects they employ epicuticular wax crystals on the inner walls of the conductive zone of the pitchers to hamper insect attachment by adhesive devices. It has been proposed that the detachment of individual crystals and the resulting contamination of adhesive organs is responsible for capturing insects. However, our results provide evidence in favour of a different mechanism, mainly based on the stability and the roughness of the waxy surface. First, we were unable to detect a large quantity of crystal fragments on the pads of insects detached from mature pitcher surfaces of Nepenthes alata. Second, investigation of the pitcher surface by focused ion beam treatment showed that the wax crystals form a compact 3D structure. Third, atomic force microscopy of the platelet-shaped crystals revealed that the crystals are mechanically stable, rendering crystal detachment by insect pads unlikely. Fourth, the surface profile parameters of the wax layer showed striking similarities to those of polishing paper with low grain size. By measuring friction forces of insects on this artificial surface we demonstrate that microscopic roughness alone is sufficient to minimize insect attachment. A theoretical model shows that surface roughness within a certain length scale will prevent adhesion by being too rough for adhesive pads but not rough enough for claws." [from Conclusion] In conclusion we cannot rule out the possibility that to a certain degree breaking of extensively protruding single wax crystals may occur and consequently be found as residues attached to the tarsi. Presumably this would increase the anti-adhesive effect of the surface of N. alata. Furthermore, breaking of crystals for catching prey may occur in different species of pitcher plants or even individuals of N. alata under certain circumstances or environmental conditions. However, the results presented clearly indicate that the structural properties of the mechanically very stabile epicuticular wax alone are sufficient to prevent insect adhesion to the conductive zone of N. alata. (Scholz et al. 2010:1115,1125)

The Private Life of PlantsAugust 21, 1995
David Attenborough

Journal article
Slippery surfaces of pitcher plants: Nepenthes wax crystals minimize insect attachment via microscopic surface roughnessJournal of Experimental BiologyMarch 12, 2010
I. Scholz, M. Buckins, L. Dolge, T. Erlinghagen, A. Weth, F. Hischen, J. Mayer, S. Hoffmann, M. Riederer, M. Riedel, W. Baumgartner

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Tropical Pitcher PlantsNepenthesGenus

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