Libre (free/open source) software is becoming an increasingly important component of today's software industry. While many studies have focused on the inner working of a few successful projects, few have paid attention to explain how it comes to be in the big sense. This is probably due to its distributed and mostly non-controlled development nature, that makes it difficult to be understood and researched. This paper proposes an analogy of the libre software phenomenon and the way some social insects perform large-scale works. The analogy is based on the stigmergy concept, which states that communication (by means of stimulus) does not happen directly among entities (in our case developers) but through changes in the environment. Stigmergy makes an autocatalytic reaction possible as it has been observed in bazaar-driven self-organized libre software projects. We will build a model based upon these ideas, test it against data and results from previous research and provide results of a simulation of our proposed model. Our conclusion is that the libre software phenomenon can indeed be modeled as a stigmergic one. Among other things this means that the individual productivity as a whole may not be as important as the total production of a community; which, in turn, means that stigmergic mechanisms should be used in order to increase productivity.