Hi @agmoore! certainly, there are very few insects that humans do not squash when they see them near or inside the house. On the other hand, if it is possible that there are both fly larvae and these beetles in the same excrement, so competition for this resource is possible; however, these beetles select very well the portion of the excrement they are going to use, being very unlikely that they take fly larvae to their nests and, if so, these will die for being underground. In turn, all living things are essential to the proper functioning of natural systems, including flies as decomposers and staple food for a large number of living things. Thank you very much for your visit! :)