Probably the most important part of our strategy is the "keeper" structure.
This consists of 7 ants surrounding an empty square on our base, like so:

(ants are X or Y)

 # # . Y X X + + + . .
  # . X + X + + + + . .
 # . X X + + + + + + .
  . + + + + + + + + + .
 . + + + + + + + + + +
  + + + + + + + + + + +
 . + + + + + + + + + +
  . + + + + + + + + + .
 . . + + + + + + + + .
  . . + + + + + + + . .
 . . . + + + + + + . .

This is constructed at the beginning by everyone turning left two (so
that the ant marked Y is the lowest ID, to simplify the code - see
startup.txt) and then doing a bit of looking to figure out which ant is
which. Everyone else disappears off in all 6 directions once the keeper
is setup.

The ants marked X sit there all game; ants returning with food are
directed by marks into the structure via the only entrance. Each one drops its
food, and the ant marked Y sees this, turns round, waits a bit for the 
delivering ant to finish resting, and goes off to hunt food. The ant that
just dropped food moves forward into that spot and takes up the function
of Y.

The idea of this strategy is that it makes it highly unlikely that we
will have food stolen.