void setup() {
  size(500, 200);
  fill(0, 200, 0);
  caterpillar(50, 50, 20, 10);
  caterpillar(50, 100, 10, 5);
  fill(255, 255, 0);
  caterpillar(100, 150, 10, 10);
}

/*
   Render a caterpillar with n overlapping body segments,
   each with radius r, and with the head at the left end,
   centered at (x,y).
*/
void caterpillar(int x, int y, int r, int n) {
  float space = r;
  for (int k=r-1; k >= 0; k--) {
    ellipse(x+k*space, y, 2*r, 2*r);
  }
  pushStyle();
  fill(0);
  ellipse(x-r/4, y-r/4, r/5, r/5);
  ellipse(x+r/4, y-r/4, r/5, r/5);
  popStyle();
}