The model organism Caenorhabditis elegans was utilized to determine, in vivo, the mode(s) of action of four plant polyphenols, namely, tannic acid (TA), gallic acid (GA), ellagic acid (EA), and catechin (CT). The determination of lifespan, stress resistance, growth, reproduction, eating-related behaviors, antioxidative capacities, and lifespan assays with the mev-1 and the eat-2 mutants as well as in the presence of dead bacteria provided new insights into their action. All four compounds prolonged lifespan, but only TA and CT mediated distinct stress protection. Longevity is unlikely the result of antioxidant capacities but rather due to calorie restriction imitating and hormetic properties in the case of TA and EA or antimicrobial capacities of GA and EA. Furthermore, the prominent "disposable soma theory" is only partly reflected by these polyphenols. In summary, this study underlines the diversity of polyphenolic phytochemicals and their mechanistic background.