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Defense and Attack Strategies and Mechanisms in Biology 351

Figure 13.3 A pitcher plant trap, which is a modified leaf. The rim of the trap is curled over, forming a slippery
platform onto which insects can walk.

The Peripatus (the velvet worm, Figure 13.4) shoots out sticky adhesive threads that entangle
its prey. The threads contain protein, sugar, lipid, and a surfactant, nonylphenol. The proteins
are the principal component of the slime; the amino acid composition suggests collagen. The
original function of the secretion was probably defense, developing into attack as the viscosity,
amount, and distance that the substance could be expelled all increased. This defensive substance
would in turn be also useful for hunting, if the original condition consisted of capturing prey
directly using mandibles, as when onychophorans handle small prey. The adhesive substance
probably allows the entanglement of larger and therefore more nutritious prey (Benkendorff et al.,
1999).
When in danger, some species discharge sticky threads that can entangle predators. Some like
the sea cucumber can even expel their internal organs, which they regrow causing it no harm at all.
Although the mechanical properties of the threads have not been measured, they are obviously very

Figure 13.4 The velvet worm, Peripatus capensis. It lives in damp places and has no external armor. However, it
can shoot sticky threads several times its body length.