This work studies some aspects of life cycle morphology and intrapopulational variability of a laboratory strain of Tyrophagus putrescentiae (Schrank, 1758), type-species of the genus Tyrophagus Oudemans, 1924 (Acari, Acaridae). External attributes agree with previous descriptions. The preapical process on tibia and genu IV is described for the first time in this species. Mating females show a depression of the postanal cuticle, which seems to be a topographic reference for seminal reception organs. A key for motile stages of this species, based in the chaetotaxy and differential attributes between sexes, is presented. The study of 43 numeric variables, show: (i) the possibility to establish a model of three categories of variables (populational, sexual primary and sexual secondary), which are the numerical representation for the traditional concepts of sexual homomorphism, sexual primary dimorphism and secondary sexual dimorphism; and (ii) the factors pigmentation and female gravid state define a second type of intrapopulational variability within the adult life history. This model may represent an instrument to clarify the systematic, diagnostic, ecological and taxonomic relatedness of groups belonging to the family Acaridae and the major group Astigmata.