The house fly (Musca domestica L.) is a well-established vector of human pathogens, including Campylobacter spp., which can cause infection of broiler chicken flocks, and through contaminated broiler meat can cause outbreaks of campylobacteriosis in humans. We investigated whether Campylobacter jejuni (Jones) could be transferred between life stages of M. domestica (larvae-pupae-adults) and determined bacterial counts of C. jejuni at different time points after bacterial exposure. C. jejuni was transmitted from infected larvae to pupae, but not to the adult stage. Infected larvae maintained at 25°C had mean bacterial numbers of 6.5 ± 0.2 SE log₁₀ (colony forming units [CFU]/g) that subsequently dropped to 3.6 ± 0.3 SE log₁₀ (CFU/g) 8 h after infection. Pupae originating from infected larvae contained mean bacterial numbers of 5.3 ± 0.1 SE log₁₀ (CFU/g), and these numbers dropped to 4.8 ± 0.1 SE log₁₀ (CFU/g) 24 h after pupation. The decline in C. jejuni numbers during pupal development coincided with increased expression of antimicrobial peptides, including cecropin, diptericin, attacin, and defensin, in the larva-pupa transition stage and a later second peak in older pupae (4 or 48 h). Conversely, there was a reduced expression of the digestive enzyme, lysozyme, in pupae and adults compared with larvae.