Biomedical Engineering Reference
In-Depth Information
industry could learn from the different ways
that stigmergy is applied in insect colonies.
Graffiti and littering by human beings also
have stigmergy characteristics. Places where
graffiti and litter emerge seem to attract more of
the same. Railway companies therefore have the
anti-graffiti strategy to remove the graffiti as
quickly as possible. By removing the traces of
other
members of the tribe,
it is believed that the
undesired decorations will be kept at a
minimum.
per hours on paths over 100 m in length
[28]
.
These ants solve the traffic problem in a way that
is similar to how we structure our road systems.
They form distinct lanes, where the inbound
traffic of foragers returning to the nest with prey
takes place in a central lane and outbound forag-
ers move in two bands on either side of the cen-
tral lane. This has the added benefit that the ants
carrying valuable prey items are better protected
from predators. The separation of flow is formed
by individual workers following simple interac-
tion rules and having asymmetric turning rates,
where returning workers with prey have a lower
turning rate than outgoing ants, as illustrated in
Figure 13.7
[28]
.
However, most ants do not separate flow into
specific lanes like the army ants. Instead they
rely on other traffic-control rules. For the Euro-
pean black garden ant,
Lasius niger
, one path is
used at low densities where collision-avoidance
maneuvers of the individual ants end up avoid-
ing the formation of traffic jams. However, as the
density of workers in the path builds up, a new
separate path is formed before the density gets
so high that significant delays from traffic jams
can occur
[29]
. Again, this bifurcation arises as a
result of the behavioral rules of the individual
worker ants in that at higher densities ants start
to push oncoming ants onto another path.
Swarm-intelligence principles inspired by the
collective insect societies are used for develop-
ing computer algorithms and motion control
principles for robotics. The basic idea is that a
swarm of individuals can coordinate and behave
as a single entity that performs better than the
individuals. Using cooperative behavior, the
individuals help each other and solve problems
that cannot be handled by the single individu-
als. Such a collection of cooperating robots is
referred to as a
swarm-bot
[30-32]
. Because the
individual robots in the swarm can communi-
cate with simple sensors such as light and sound,
they stay together and avoid barriers such as
walls and holes
[31, 32]
.
1
3.5 SWARM INTELLIGENC
E
Swarm intelligence
is the seemingly intelligent
behavior that emerges from the collective behav-
ior of a large number of autonomous agents.
In biology, this term is most widely used with
reference to the colony-level behaviors seen in
social insects. For instance, whereas individual
fire ants (
Solenopsis invicta
) struggle and rela-
tively rapidly drown after falling into a pool of
water, groups of fire ants link together to form
rafts that can float on the water surface for days
[26]
. Similarly, army ants in their migratory
phase will fabricate temporary nests (bivouacs)
consisting of several hundred thousand work-
ers linking their bodies together to protect the
queen and the brood
[27]
. However, where this
collective behavior is perhaps the most impres-
sive and the most biomimetically relevant is in
the large-scale traffic control of foraging ants.
Most ant species use specific paths that lead
from the nest to the foraging site, which, due to
attraction of previous workers' pheromone, is
chosen by almost all foraging ants. Thus at any
given moment, a large number of foragers are
moving toward the food source and simultane-
ously a similar number are moving in the oppo-
site direction toward the nest. In one group of
ants, the army ants, the potential for collisions
and traffic jams is particularly large. Colonies of
army ants,
Eciton burchelli
, have more than
200,000 foragers and carry over 3,000 prey items
