There remains considerable debate about the ideal level of taxonomic resolution needed in bioassessment. What is most often cited is the trade off between the expenses associated with genus/species level taxonomic work versus the “costs” associated with information loss when higher taxonomic levels are used. In reality, we know very little about variability within and among lineages particularly in the context of stressor –specific responses to environmental stressors. This is largely because hypotheses generated from field studies are rarely tested in a controlled environment.  Here we present physiological data relevant to cadmium susceptibility in 21 insect species representing 3 major orders (Ephemeroptera, Plecoptera, Trichoptera) 8 families and 18 genera. As expected, tremendous variation was observed within orders.  At the family level, physiological responses were more inconsistent, with little variability exhibited in some families, while others were remarkably variable.  More closely related taxa (congeners) tended to be similar in their handling of Cd.  Here we rank 21 species in terms of their susceptibility to dissolved Cd exposures by examining uptake, efflux and sub-cellular compartmentalization, and compare these rankings to tolerance values. The implications of these data in terms of bioassessment will be discussed.