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358 Biomimetics: Biologically Inspired Technologies

13.8.2 Cloggers

Polymer agents, sticky-soft plastics, used in burst munitions to clog up jet and tank engine intakes
(Alexander et al., 1996).
Hagfish slime is a mixture of mucus and threadlike fibres, secreted in concentrated form from
pores on the side of the hagfish’s body. Upon contact with the seawater, the slime absorbs water
rapidly, expands into a sticky gel that can ensnare and sometimes suffocate an attacker. Up to 5 l
of gel can be produced within seconds (Koch et al., 1991). We are probably missing a trick by
producing only single-phase ‘‘cloggers.’’ The addition of fibres would greatly increase the coher-
ence of the clogging substrate, generating a compliant fibrous composite material.
The hagfish rids itself of the mucus by tying itself into a knot that it runs down its body pushing
the mucus ahead of it (Fernholm, 1981). Over the ranges of temperature encountered by the hagfish,
the gel strength is relatively independent of temperature, which perhaps ensures that slime is an
effective defense in a variety of conditions.

13.9 PROJECTILE

13.9.1 Water Stream

Mobile unit that projects a continuing stream of water for riot control purposes (Alexander
et al., 1996).
The archer fish (Toxotes jaculator) is the best-known analog, though it conserves its energy by
aiming the jet of water very carefully and bringing down one object at a time. The object is usually an
insect or other small animal sitting on a plant overhanging the water. With the tongue against a
groove on the roof of the mouth, the fish forms a tube, and forces water out by snapping the gills shut.
The jet of water is directed with the tip of the tongue. The fish can squirt up to seven times in quick
succession, and the jet can reach 2 to 3 m, but it is accurate to only 1 to 1.5 m. Fish as small as 2 to 3 cm
long can already spit, but their jets reach only 10 to 20 cm (Rossel et al., 2002). The disadvantage
of this technique is obviously that when the dislodged prey falls into the water, it can be taken by
any of the other fish. So the archer tends to position itself below the prey, and also knows how to
catch an object falling on a curved trajectory, a skill that would make it a good ball player!

13.10 RIOT CONTROL AGENT

13.10.1 Chemical Mace

Small spray can containing a 0.9% solution of agent CN in a variety of petroleum-based carriers
including a mixed freon/hydrocarbon solvent. First introduced in 1966. CSMace then developed in
1968 by suggestion of the U.S. Army (Alexander et al., 1996).
Chemical agents produced by animals or plants tend to be for defense, sometimes against a
single individual and sometimes against large numbers. Carnivorous ground- and water-beetles
(Adephaga) are some of the better known animals that deliver compounds in one of three ways:

(1) Oozing: The glands of many beetles do not have muscles for discharging large amounts of
substance and so the material only oozes out from the openings. This is helped by internal pressure.
(2) Forceful spraying: Many ground beetles have intrinsic muscles with the glands. The beetle
Pasimachus subsulcatus can forcibly discharge a spray up to several centimetres that is irritating
to the eyes and hurts abraded skin.
(3) Crepitation or squirting is characteristic of bombardier beetles (q.v.). Hydroquinones are stored
with hydrogen peroxide in the major gland chambers and the ezymes catalase (which converts