The article shows the results of set of experiments with laboratory strains of Musca domestica L. demonstrating high level of polymorphism and differentiation in the initial population (strain Cooper) by sign of adults' life span (LS). Possibility of LS indices extension as a consequence of hormesis caused by a short-term contact with the toxic compound (piperonylbutoxide) has been illustrated. Limitations of LS changes defined by species genotype characteristics have been established.