Keeping in mind that no one is in charge of a colony and that there is no central plan,
how do the ants adjust their reconnaissance if their territory expands or shrinks?
"No ant told them, 'OK, guys, if the arena is 20 by 20. . . .' Somehow there has to
be some rule that individual ants use in deciding to change the shape of
their paths so they cover the areas effectively.
I think that that rule is the rate in which they bump into each other."
The more crowded they are, the more often each ant will bump into another ant.
If the area of their territory is expanded, the frequency of contact decreases. Perhaps,
Gordon thinks, each ant has a threshold for normality and adjusts its path shape
depending on how often the number of encounters exceeds or falls short of that threshold.
If the territory shrinks, the number of contacts increases and the ant alters its search pattern.
If it expands, contact decreases and it alters the pattern a different way.
In the Arizona harvester ants, Gordon studies tasks besides patrolling. Each ant has a job.
"I divide the tasks into four: foraging, nest maintenance, midden piling refuse,
including husks of seeds] and patrolling - patrollers are the ones that come out
first in the morning and look for food. The foragers go where the patrollers find food.
"The colony has about eight different foraging paths. Every day it uses several of them.
The patrollers go out first on the trails and they attract each other when they find food.
By the end of an hour's patrolling, most patrollers are on just a few trails. . . .
All the foragers have to do is go where there are the most patrollers."
Each ant has its prescribed task, but the ants can switch tasks if the collective needs it.
An ant on housekeeping duty will decide to forage. No one told it to do
so and Gordon and other entomologists don't know how that happens.
"No ant can possibly know how much food everybody is collecting,
how many foragers are needed," she said. "An ant has to have very simple rules that tell it,
'OK, switch and start foraging.' But an ant can't assess globally how much food the colony needs.
"I've done perturbation experiments in which I marked ants according to what task they're doing
on a given day. The ants that were foraging for food were green, those that were cleaning the nest
were blue and so on. Then I created some new situation in the environment; for example,
I create a mess that the nest maintenance workers have to clean up or
I'll put out extra food that attracts more foragers.
"It turns out that ants that were marked doing a certain task
one day switch to do a different task when conditions change."
Of about 8,000 species of ants, only about 10 percent have been studied thus far.
"It's hard to generalize anything about the behavior of ants," Gordon said.
"Most of what we know about ants is true of a very, very small number
of species compared to the number of species out there."