Colloquium: Emergent Fire Ant Towers: An Adventure in Experimentation And Math Modeling

Computer Science Department Colloquium

Title: Emergent Fire Ant Towers:  An Adventure in Experimentation
       And Math Modeling

Speaker: Professor Craig A. Tovey

Affiliation: School of Industrial and Systems Engineering
             Georgia Institute of Technology

Host: Professor Judy Goldsmith

Time and Date: 3:00-4:00PM, Friday, February 13, 2015

Location: Marksbury Theater, some refreshments are expected.


Fire ants, Solenopsis Invicta, link their bodies together to form
various  assemblages.  We study the construction of their ant towers,
built around a branch or other supporting structure  when an ant raft
docks to land or when alternative shelter cannot be found.  We idealize
the tower as comprising layers of annuli whose diameters decrease as
their height increases.  Using the  simple assumption first proposed by
Timoshenko in 1930,  that each ant bears an equal load  of other ants,
we accurately predict the tower's bell shape for varying numbers of
ants. The bell shape diverts falling water droplets.  Similar shapes are
found in man-made structures such as Spanish Castells, southeast Asian
Buddhist stupas, and zombie towers.  We mathematically model the rate of
tower construction as limited by the bottleneck step of filling in the
inner ring of each layer.  Without a complete inner ring the tower can
partially peel off and fall.  Our model uses a single parameter measured
from experiment, the expected time for a ring slot to be filled.  It
predicts that towers with larger inner diameter will grow less quickly.
This prediction proves to be quantitatively quite accurate for the range
3mm to 14 mm in a series of additional experimental trials.
Serendipitous time-lapse photography and novel X-ray tracking reveal
that the tower is constantly sinking and being rebuilt as ants leave the
base through tunnels and fill in unoccupied space at the top.  Once
built, the tower structure is static, but the ants circulate through it.
The  individual ant behaviors that have previously been used to
accurately explain the shape and growth rate of ant rafts, together with
their observed physical constraints and well-known tunneling, suffice to
explain accurately the growth rate of their towers.   The principles
found here may help in understanding natural and engineered swarms that
must form different structures in different environments.


Craig Tovey is the David M. McKenney Family Professor in ISyE at Georgia Tech. He received an A.B. in applied mathematics from Harvard College in 1977 and both an M.S. in computer science and a Ph.D. in operations research from Stanford University in 1981. Dr. Tovey's principal research and teaching activities are in operations research and its interdisciplinary applications to social and natural systems, with emphasis on sustainability, the environment, and energy. He co-directs CBID, the Georgia Tech Center for Biologically Inspired Design. His current research concerns inverse optimization for electric grid management, classical and biomimetic algorithms for robots and webhosting, the behavior of animal groups, sustainability measurement, and political polarization. Tovey received a Presidential Young Investigator Award in 1985 and the 1989 Jacob Wolfowitz Prize for research in heuristics. He was granted a Senior Research Associateship from the National Research Council in 1990, was named an Institute Fellow at Georgia Tech in 1994, and received the Class of 1934 Outstanding Interdisciplinary Activity Award in 2011.