Abstract Attacks by wolves (Canis lupus) on dogs (C. familiaris) presumably are motivated both by preying and elimination of potential competitors. Regardless of these alternative motivations in wolves, the risk of attacks might be higher when the density of primary prey is low. We examined how many dogs do territorial wolves in Finland kill in relation to the population density of the most abundant ungulates, moose (Alces alces), white-tailed deer (Odocoileus virginianus), and roe deer (Capreolus capreolus). Most attacks by wolves on dogs take place in hunting with dogs. The number of wolf-killed dogs was in highly significant negative relationship to the population density of white-tailed deer and to total ungulate biomass per unit area which is largely determined by the density of white-tailed deer. Our results indicate that abundant wild prey would decrease the risk at which wolves attack dogs. On the other side of the coin prevail two hard facts which wildlife managers had to take a notice. White-tailed deer, although a potential mitigator of wolf–human conflict, is an alien species and a partner in > 6000 traffic collisions annually in Finland. One factor that seemed to increase the risk of wolf attacks on dogs is the low ungulate density in regions where moose is the only remarkable ungulate prey. Higher moose densities could decrease the risk of attacks, but on the other hand, higher densities could increase the risk of serious traffic collisions and browsing damages in forests.