How much do the chemical trails speed up the colony's foraging? Green chemical trails form between the purple nest and the nearest blue pile (food-pile1, to the right) and fade once that pile is empty.
Try this Set evaporation-rate to 99 and run from the start, so trails vanish almost as soon as they are laid. food-pile1 now takes roughly 900 to 1,200 ticks to empty instead of about 200, and the piles no longer empty nearest-first. The rate is read every tick, so you can also change it mid-run.
About this model Where it ends up
Uri Wilensky's Ants model (NetLogo Models Library, 1997). A colony forages with only local cues. Ants carrying food lay a chemical that spreads and evaporates, and searching ants turn toward it, so a pile one ant finds is soon being worked by many.
The nest is a disc of radius 5 at the center; three piles of the same size sit about 21, 30 and 40 patches away, with one unit of food per patch (81 per pile). Each patch stores nest-scent (200 minus its distance from the nest) and a chemical level. Ants leave the nest one per tick. Each tick, in random order: a searching ant on food takes one unit and turns around; otherwise, if the chemical under it is between 0.05 and 2, it turns toward the highest of the patches ahead and 45° to either side. A carrying ant on the nest drops its load and turns around; otherwise it adds 60 chemical to its patch and steers up nest-scent the same way. Moving ants then turn randomly by up to 40° either way and step forward 1. Finally each patch shares diffusion-rate percent of its chemical with its 8 neighbors and loses evaporation-rate percent. Both rates are read every tick; population only at setup.
NetLogo's piles hold 1 or 2 units of food per patch; here each food patch holds one. NetLogo's ants also turn around when they can't move forward, while these are stopped at the world edge until their heading changes.
