Ants At Work

Fres 1010, Fall 2005Complex Adaptive Systems

Lecture 2Eileen Kraemer

Why study ants?

How are these related? Behavior of individual ants (microbehavior) Overall behavior of colony

An emergent, self-organizing system

Deborah Gordon

Researcher at Stanford University Tracks life cycles of ant colonies,

following them year after year as they Look for food Compete with other colonies Mate with other colonies

Author of Ants at Work: How an Insect Colony is Organized

Various Networks of Ants

Networks and connections within the ant colony.

Networks of trails and paths to food outside the colony.

Networking and connections with neighboring ant colonies.

3 Distinct Levels of Ants

Queen Ants

Worker Ants Sterile Females

Male Ants

Queen Ants

Not an authority figure; doesn’t decide which worker does what

Lays eggs Fed and cared for by “interior”

workers

The “Escape Hatch”

In case of disturbance, interior workers carry the Queen Ant down a passageway that leads two feet underground

Why? Queen Ant “orders” them to? Their genes “tell them to” – it is in the best

interest of the colony (and the colony’s gene pool) because the Queen is responsible for giving birth to members of the colony

Working Ants and Daily Chores

Interior Workers Tend to the Queen and brood (eggs, larvae, and

pupae) Nest Maintenance

Open and close entrances to the nest Maintain all structures and pathways within the

colony Patrollers

Designate the foraging paths for the day Foragers

Follow paths designated for them to gather food for the colony

Midden Workers Manage the refuse pile, also known as the Midden

The Midden also seems to have a significant relation to how the ants find their colony.

Allocation of Tasks No source of leadership

Queen is only there to reproduce, not to control the colony

As conditions change emphasis on certain jobs change Workers are moved from one task to

another depending on the need for workers Ex. If there are serious issues with nest

maintenance, some foragers will switch to nest maintenance until the problem is solved.

Foraging is the most important task and will call for workers before any other task

Foraging Paths and Trails

Mature colonies can have up to 8 customary foraging trails

However, patrolling ants generally do not send foraging ants to the same trail as the day before

Younger colonies are more likely to send their foraging ants to a rich food source they had once found

Foraging Paths (continued) Larger colonies don’t

necessarily cover larger areas, but get more food because they have more workers

Paths are very adaptable They grow into more

intricate paths with the growth of the workforce

A small workforce changes the paths to a more standard construct to cover area more effectively

Ants partition their living space

Ants take trash from food they’ve collected and deposit it in the midden (garbage dump)

Ant carcasses piled into a “cemetery” In closed environment:

Cemetery is farthest point from colony Midden is half-way between cemetery and

colony

Ants also …

Find the shortest distance to a food source

Prioritize food sources Switch from nest-building to foraging to

raising ant pupae

How ???

How do they know to do that???

How do they accomplish it?

How do they do that?

Swarm logic: “thousands of ants, each limited to a meager vocabulary of pheromones and minimal cognitive skills collectively engage in nuanced and improvisational problem-solving.”

Individual ants assess local conditions and respond, interactions among ants result in global (colony) behavior

Foraging <-> colony size

Number of ants foraging for food is constantly adjusted, based on: Overall colony size Food available in surrounding area Presence of other colonies in vicinity

How do ants know to change jobs?

Ants communicate

Pheromones (semiochemicals) Secreted from sternal and rectal glands Play the central role in the organization of

colonies (Wilson & Holldobler)

Also regurgitate recently digested food Tactile

Pheromones can signal:

Task-recognition “I’m on foraging duty.”

Trail attraction “There’s food over here!”

Alarm behavior “Run away!”

Necrophoric behavior “Let’s get rid of these dead ants.”

Seems too simple ….

Can also detect gradients in pheromones Essential for forming food delivery lines Provides directional information

Can also detect frequency of detection Encounter 10 other foraging ants/hour -> keep at it Encounter 100 other foraging ants/hour -> change

jobs Estimate size of colony by statistical sampling of

encounters???

Principles for deriving global intelligence from local interactions

More is different Ignorance is useful Encourage random encounters Look for patterns in the signs Pay attention to your neighbors

More is different

Must have a critical mass of ants for colony to make intelligent assessments of local state 10 ants – not enough for interactions to happen frequently

enough for organized behavior to emerge 2000 ants – that’s enough!

Ants don’t “know” they’re prioritizing pathways between different food sources by laying down pheromones … and we wouldn’t know either if we only studied individual

ants …it is only by observing entire system that behavior becomes apparent.

Ignorance is useful

Each ant follows simple rules Complex analysis not required of

individual ants; don’t become too finely tuned ….

Variations in response among ants helps to smooth transitions of colony behavior

Encourage random encounters

Colonies rely on random interaction of ants exploring space without any predefined orders.

Arbitrary pair-wise encounters; large number of encounters allows individuals to gauge system state

Response of individuals combine to alter system state

Supports adaptation to new environmental conditions

Look for patterns in the signs

Ants have small vocabulary Rely on patterns in semiochemicals

they detect Gradient in pheromone trail -> leads to

food source High ratio of nest-builders to foragers in

other ants they encounter -> switch to foraging

Pay attention to your neighbors

Local information can lead to global wisdom.

Primary mechanism of swarm logic is the interaction of neighboring ants in the field.

Life Cycles Colony Life Cycles

Form when a New Queen mates with a Male from another parent colony, and then forms her own colony

Generally last about 15 years Can exist as long as the Queen can continue

reproducing female workers Individual Ant Life Cycles

Queen: 15- 20 years Males: A few weeks (long enough to reproduce) Female Workers: About 1 year

Stages in Colony Development

Infancy Adolescence Maturity

Differences among life stages

Younger colonies are more fickle than older colonies – may respond differently from week to week.

Encounters with other colonies: Older colonies avoid interaction. Younger colonies more aggressive.

Are the ants older too?

Male ants live only one day. Worker ants live about 12 months. Queen ant lives for years. So, if the ants are just as young, why

does an older colony behave differently from a younger colony?

Connections with Other Colonies

Workers can recognize ants from their own colony by a colony specific scent

When foragers from different colonies meet, those foraging trails will be used less and less, and seen as space lost to competition

Certain foragers specialize in fighting, and do not usually go out unless large number of foragers are out

Older Colonies vs. Younger Colonies

Older colonies are more likely to interact with other colonies Colonies remain about the same size

Once colonies reach the 2-year mark they are likely to keep the size of their nest the same

More ants are sent out from the older colony

Older colonies also send their foragers out farther distance

Natural Response to Strangers Ants respond to the rate of interaction

with non-nestmates Sight not good, use contact rate to

determine the density of non-nestmates Ants will try to maintain density through

clustering when they feel contact rate is low

Contact rate directly correlates with density of nestmates Low contact rates indicates high numbers of

mates present High contact rates indicate low number of

mates present

Sources Used Gordon, D. (1999). Ants at work.

New York, NY: The Free Press. Foster, D. (2001) An ant’s life.

Retrieved from the World Wide Web on November 13, 2002.

Library.Thinkquest.org. (?). Insects. Retrieved from the World Wide Web on November 13, 2002.

The University of Georgia College of Agricultural and Environmental Sciences. (2000). Managing imported fire ants in urban areas. Retrieved from the World Wide Web on November 13, 2002.