We present a model for the travelling salesman problem (TSP) solved using the ant colony optimisation (ACO), a bio-inspired mechanism that helps speed up the search for a solution and that can be applied to many other problems. The natural complexity of the TSP combined with the self-organisation and emergent behaviours that result from the application of the ACO make model-checking this system a hard task. We discuss our approach for modelling the ACO in a well-known probabilistic model checker and describe results of verifications carried out using our model and a couple of probabilistic temporal properties. These results demonstrate not only the effectiveness of the ACO applied to the TSP, but also that our modelling approach for the ACO produces the expected behaviour. It also indicates that the same modelling could be used in other scenarios.