It is now fairly well known that any animal study of longevity has to be controlled for calorie restriction, as the effects of even a modest change in dietary intake can outweigh the intended effects of the study, rendering the results useless. This is far from the only confounding factor out there, however. Here is some work on a different issue that might be problematic for longevity studies in worms: "The nematode worm Caenorhabditis elegans has been used to identify hundreds of genes that influence longevity and thereby demonstrate the strong influence of genetics on lifespan determination. In order to simplify lifespan studies in worms, many researchers have employed 5-fluoro-2'-deoxyuridine (FUdR) to inhibit the development of progeny. While FUdR has little impact on the lifespan of wild-type worms, we demonstrate that FUdR causes a dramatic, dose-dependent, twofold increase in the lifespan of the mitochondrial mutant gas-1. Thus, the concentration of FUdR employed in a lifespan study can determine whether a particular strain is long-lived or short-lived compared to wild-type." This sort of thing is one of the many reasons why it is better to weigh evidence across many studies and to be skeptical of any one study in isolation.