During civil wars, some communities raise self-defense militias to protect themselves from insurgent predation, but these militias can end up mutating into predatory organizations. The extant literature has focused chiefly on the predatory propensity of state-created self-defense militias and has mostly overlooked why some community-created self-defense militias segue into predatory organizations while others eschew predation altogether. This study explains this phenomenon, drawing on in-depth interviews with active members of two community-created self-defense militias (Ahlu Sunna Waljama’a and Macawiisley) in Somalia. In doing so, two sequential mechanisms (sponsorship and mobility) that determine the propensity of predatory behavior are introduced. Self-defense militias that conduct offensive operations engage in predatory behavior, irrespective of whether they are sponsored locally or have external patrons. Externally sponsored self-defense militias that engage in offensive operations attract opportunistic recruits and become motivated by material benefits, while community-sponsored self-defense militias that conduct offensive operations instrumentalize their position to settle old scores against rival communities. By contrast, self-defense militias that restrict their operations to defensive activities typically recruit dedicated homegrown members, and are regulated by community-managed accountability mechanisms that prevent predatory and abusive behavior. This community control remains crucial for defensive self-defense militias, who must balance external patrons’ strategic aims with their local objectives.