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360 Biomimetics: Biologically Inspired Technologies

Figure 13.7 The South American peacock butterfly Automeris memusae, showing its cryptic- (above) and
warning- or flash- (below) wing positions.

called nematocysts about 5 mm across. Each capsule contains a coiled hollow thread with a barb at
the end. The capsules contain a poison capable of paralysing or killing small animals. When a small
animal contacts the tentacles, the capsules are triggered and fire their barbed threads like harpoons,
which pierce the skin of the animal and inject their poison. In the fresh-water polyp Hydra vulgaris,
the capsule contains a 2 M salt solution and so reaches a turgor pressure of 150 atmospheres (15
MPa) before it shoots out the dart at an acceleration of 40,000 g (Holstein et al., 1994). The sea
anemone uses its stinging cells for defense, as do other animals. The digestive tract of the
nudibranch sea slug Aeolidia (a sort of snail) is lined with a protective coating to prevent injury
from any unactivated nematocysts it consumes, which it then transports into its skin to use for its
own defense. Sea anemones also use their poisonous stings against their own kind, usually while
competing for territory. Some species even possess special club-like structures, packed with potent
stinging capsules, that they use to battle other anemones. Territorial fights often result in serious
injury and even death to one or both anemones.
13.12.2 Diversion

A diversion that acts directly by affecting one or more of the five senses. Noise that lasts less than
one second (Alexander et al., 1996).
An obvious example from biology is flash coloration and its commonest manifestation is in the
hind wings of cryptically colored moths with brightly colored hind wings that are revealed suddenly
when the insect is threatened. The hind wings can be of one or two colors in well-defined patches
(often red or yellow with black) or have large and colorful eyespots (Figure 13.7). Another well-
known example is feigning injury; the lapwing nests on the ground and will lure a potential predator
away from its nest by dragging one wing on the ground with the pretence that it is broken. When the
predator is safely away from the nest, the lapwing flies away.

13.13 SURVEILLANCE

13.13.1 Electrosensing

A ‘sixth sense’ based on reception of electrical signals in the environment. Akin to electronic
eavesdropping.
Teleost (bony) fish, elasmobranchs (sharks and rays) and the duckbilled platypus (and probably
many more types of animals) have an electric sense. It is best developed in the elasmobranchs,
which have rows of pit organs (ampullae of Lorenzini) that can detect electric fields as weak as