Achilles: When there aren't enough ants to keep the thing rolling?
Anteater: Exactly. The other thing that can happen is that a critical mass of ants is present, and the thing will snowball, bringing more and more ants into the picture. In the latter case, a whole "team" is brought into being which works on a single project. That project might be trail-making, or food-gathering, or it might involve nest-keeping. Despite the extreme simplicity of this scheme on a small scale, it can give rise to very complex consequences on a larger scale...
(C) Douglas R.Hofstadter - Goedel, Escher, Bach: an Eternal Golden Braid.
This description appears to be perfectly applicable to the open-source projects, too ;)