Ants' Efficiency Inspires Supply Chain Experts

Barbara Christopher
Industrial and Systems Engineering
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What do ants and workers at Subway have in common?

A method of efficiently coordinating the transfer of food. In the case of
ants, it's moving food to the nest. In the case of Subway workers, it's quickly
delivering custom-made sandwiches to hungry customers.

Both employ bucket
. Workers hand off food one to another, much like firefighters
once did with buckets of water to extinguish a blaze before pumps were invented.

It's an incredibly efficient -- yet simple -- way of moving goods, one that
businesses are adopting to help improve their supply chains and their bottom

Executives at businesses such as Subway or CVS might never have bored into
anthills for business lessons before they met John
J. Bartholdi III

Bartholdi is director of Georgia Tech's Logistics
, founded in 1992 to provide cutting-edge research in the field.

The businesses sought out Bartholdi, along with a former
graduate student, Don Eisenstein, for their insight and got a nature lesson
in the process. Though ant-watching may seem quirky, Bartholdi's
and Eisenstein's ideas are based on mathematics and observations of workers
on assembly and distribution lines, as well as the activities of social insects
adept at organizing themselves.

"In an ant colony, there are thousands of workers, but nobody is in
charge," says Bartholdi, who collects ants from around
the world with a hand lens and tweezers, putting them into vials of alcohol. "There's
no management, no consultants, no IT department. And yet they manage to allocate
workers to tasks so that the overall organization supports the survival of
the colony."

Efficient supply chains are important with the growing geographical distances
between production and consumption. "That's why the shirt I'm wearing
was sewn in Pakistan from cotton that was grown in Texas but was purchased
from a Target in Atlanta and at a cheaper cost than a shirt 20 years ago," says Bartholdi,
who returns this week from South Africa, where he lectured on supply chains
at the University of Stellenbosch in Cape Town.

"Georgia Tech is really in the forefront of international education,
particularly in topics like logistics, which is an international activity," says Bartholdi,
who lectured in Panama last month.

Combining that worldview and his penchant for the offbeat, Bartholdi coordinates Georgia
Tech's annual Great International Package Delivery Race
. The competition
involves sending packages via DHL, FedEx and UPS to the far corners of the
world to see which firm gets to each destination first -- and to study why
the runners-up do not.

But aside from globalization, businesses want to improve operations for competitive
reasons and to bolster profits. They want to get goods to customers at the
right time, at the right point, in the right condition and at the lowest cost.
Wal-Mart, for example, is testing the use of radio frequency identification
tags in tracking the shipment of perishable items, such as fruit, with the
aim of ensuring that when they are sold in stores, they aren't overripe and
have to be discounted or discarded.

Transportation companies, such as Sandy Springs-based United Parcel Service,
have moved beyond shipping and into the logistics business to boost their revenue
and profits. They now warehouse inventory for customers, fulfill orders and
inspect, repackage and label merchandise.

Last month, for example, Philips Electronics hired UPS to do just that for
customers of its medical systems division in 50 countries. Those customers
can now get critical parts faster -- the same day, as opposed to the next business

Fixing bugs in the system

Bucket brigades are especially useful in labor-intensive distribution warehouses.
Drugstore giant CVS was among the first to test Bartholdi and
Eisenstein's idea, inspired, in part, by a species of ant, messor barbarus.

The smallest, slowest of these ants forage out farthest, and carry seed back
toward the nest. Larger, faster ants wrest the seed from the smaller ants,
toting it home. The smaller ants return to collect more seed.

"So you have exactly the bucket brigade organization in which the work
is passed from slower to faster workers," says Bartholdi,
who has about 100 ants on display on bookshelves at his home in Morningside.
(A bucket brigade simulation is available at

CVS used to put the fastest worker in the first position on the line to pick
merchandise to fill orders. That resulted in bottlenecks.

"He was picking faster than anybody downstream," says Bartholdi,
who is the Manhattan Associates professor of supply chain management at Georgia
Tech's School of Industrial and Systems Engineering. The fastest worker would
get stuck behind a slower worker and could only pick at the same speed as the
slower worker.

The solution: Move the fastest worker to the end of the line.

"Under bucket brigades, whenever the fastest worker completes work,
he goes back to get more work," Bartholdi says. "This
triggers a sequence in which each worker gives up work to the faster worker
and walks back to get work from a slower worker. The slowest worker starts
another order. They are at the beginning of the chain."

Workers prefer this because it accounts for differences in ability and differences
in customer orders, according to Bartholdi and Eisenstein,
who now is a professor of operations management at the University of Chicago.

"When workers were assigned to a fixed zone in the line, they felt isolated
and under pressure," Bartholdi says. "Working in
bucket brigades, they felt like a team. And the punchline of this story is
that CVS measured a 34 percent increase in productivity, and this cost them
nothing to implement."

Don't hold the mayo

Subway's challenge was to keep everybody busy on the line assembling sandwiches
that are all different and therefore require varying amounts of work. "The
most visible problem is you have the cashier at the end available, but all
of the waiting customers are at the start of the assembly line," Bartholdi says.

Subway tried having the last worker circle back around to the start. But
this required space to pass. And it guaranteed that no one could move faster
than the slowest worker.

"Bucket brigades turn out to be a very natural solution because it divides
the work not based on average task times -- which are meaningless because different
sandwiches are being assembled -- but on how long it actually took to spread
the mayonnaise on that last sandwich," Bartholdi says.

So the person putting on the mayonnaise for one sandwich may not necessarily
be the one putting on the mayonnaise for the next sandwich.

"A bucket brigade is dynamic," says Craig Tovey, professor of industrial
and systems engineering and computer science at Georgia Tech and a colleague
of Bartholdi's. "It is constantly adjusting itself to
the work at hand."

Boundless curiosity

Bartholdi, 59, is dynamic as well, constantly on the prowl
for ideas to solve problems.

"Like any academic, I have many things that I find fascinating that
I'm working on that nobody else does, at least for a while," says Bartholdi,
a Navy veteran who spent two tours of duty in and around Vietnam. "It
takes some time for these ideas to reach maturity."

For example, Bartholdi and a former colleague, Loren Platzman,
used mathematical objects of curiosity -- spacefilling curves -- to devise
more efficient routes for Fulton County's Meals on Wheels program, which delivers
hundreds of meals daily to shut-ins.

"We estimated it shortened the routes by at least 13 percent, which
meant they needed one fewer vehicle," Bartholdi says.

What's next on the horizon?

Bartholdi wants to figure out how cost savings can be shared
equitably along all of the nodes of a supply chain. Otherwise businesses might
not have an immediate incentive to collaborate to make improvements, figuring
the benefits might be realized downstream in a different company.

"Those methods typically have to satisfy some notions of fairness and
transparency," Bartholdi says. "And they must be
resistant to manipulation. They must be practical."

Is there something in nature that can provide answers?

"I hadn't thought of that before," says Bartholdi. "Wow!"


• Born: January 1947, San Diego

• Education: Bachelor's, master's in math, Ph.D. in industrial and
systems engineering, University of Florida.

• Family: Wife, Marian Burge, deputy director, Atlanta Legal Aid Society;
son, Gabriel, 18, student, French Culinary Institute, New York.

• Collects: Photos of badly designed elevator panels. One of the worst
is in the South parking deck at Piedmont Hospital, with each floor associated
with no fewer than four separate buttons.

• Also collects ants. "The era of big-game hunting is long gone.
But collecting ants also has its element of danger. Some ants bite, some ants
sting, and some do both. So you pick them up with tweezers, being careful not
to crush them." A favorite is the leafcutter ant, found in his backyard. "They
harvest growing vegetation, bring it back to their nests, chew it up and then
regurgitate it as a substrate on which to grow fungus. The fungus is the food
that nourishes the colony."

• In his office: Magic tricks and puzzles.

• What most people don't know: As a young adult, he studied ballet and
tap dance.

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School of Industrial and Systems Engineering (ISYE)

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  • Created By: Barbara Christopher
  • Workflow Status: Published
  • Created On: Jun 17, 2006 - 8:00pm
  • Last Updated: Oct 7, 2016 - 11:07pm