A good approach to the flies starts with combating the maggots. It should be taken into account that this does not immediately result in fewer flights. However, a preventive approach to maggots is effective, because there are not yet many flies that cause nuisance. In manure cellars it is very useful to mix the wells every 3 weeks in the summer. This is also very effective when there is suddenly a lot of nuisance from the rat tail larvae. If this is not possible due to too small an amount of manure, maggot death can be used very well. Long-acting maggot killers affect the growth mechanism of the fly larvae. The fly larvae no longer develop into pupa, but molt themselves. Long-acting agents do not immediately kill all fly larvae, so that the effect is only visible after two weeks. The advantage is that a treatment only needs to take place once every four to six weeks. Long-acting products can be used very well as a preventive measure, if fly control is started in good time, such as in the spring.