The blood-sucking stable fly (Stomoxys calcitrans) is a serious pest associated with cattle production. The species is therefore subject to intensive control efforts, primarily by means of insecticides. As chemical control may have some long-term negative side-effects, biological control applying natural enemies has for several decades attracted interest. In Denmark, experiments with massreleases of the pteromalid parasitoid Spalangia cameroni have been conducted on a number of small farms with good results. Parasitoids are now marketed, but used primarily by organic farmers since the method seems economically unattractive for conventional farmers. However, as the use of insecticides is likely to be restricted in the future, this may change the balance in favour of biological control. In order to understand how control of stable flies can be conducted most efficiently, an interactive and user-friendly simulation model, called The Fly Simulator, has been developed. The model applies experimental data on temperature-dependent development, survival and oviposition rates of stable flies and S. cameroni to predict how populations of stable flies will develop when subjected to ambient temperatures, both in absence of parasitoids or after releases of parasitoids. The model shows that flies can be suppressed if parasitoids are released in large numbers at regular intervals, i.e. by inundative releases. This makes biological control relatively expensive compared with chemical control. However, the model also points to frequent removal of manure as an effective and low-cost way of managing flies. It is therefore recommended to apply a combination of high hygienic standard and inundative releases of parasitoids to maintain stable flies at an acceptable low level.