Black soldier fly, Hermetia illucens (L.) (Diptera: Stratiomyidae), larvae are suspected to inhibit house flies, Musca domestica (L.) (Diptera: Muscidae), seeking oviposition sites. However, the mechanisms regulating these interactions are not well known. In this study, a Y-tube olfactometer was used to determine whether black soldier fly eggs, larvae, puparia (without pupae inside), adult carcasses, or resulting frass of black soldier fly decrease attractiveness of adult house flies to an oviposition substrate (i.e., sugar and wheat bran diet, used as the control). Secondly, two symbiotic bacteria associated were isolated, identified, and tested for house fly attractiveness with a Y-tube olfactometer. Thirdly, volatile organic compounds produced by swine feed before and after black soldier fly, or house fly larval digestion were analyzed with gas chromatography–mass spectrometry (GC–MS). Results indicate feed mixed with black soldier fly larval frass, and symbiotic bacteria, Paenalcaligenes sp. associated with black soldier fly, were less attractive to house flies than the control. However, another symbiotic bacterium Lysinibacillus sp. associated with black soldier fly pupae was attractive. In total, 52 volatile organic compounds were identified from treatments previously described. Quantitative differences in volatile profiles across treatments potentially explain the mechanism regulating house fly substrate choices in the presence, or absence, of black soldier fly larvae.