Due to the unique and useful properties of nanodiamonds (ND), their production and use is rapidly increasing. Thus, more of these particles will be released into the environment and organisms will inevitably be exposed to them. The current knowledge about the toxicity of ND, especially in vivo toxicity, is fragmentary. In this study, the toxicity of nanodiamonds was assessed in Acheta domesticus following chronic exposure to different nominal concentrations of ND (20 and 200 μg g−1 food) administrated in food for the entire lifespan. The activity of oxidative stress enzymes (catalase, glutathione peroxidase), total antioxidant capacity, as well as the level of heat shock protein were determined. A significant increase in all of the measured parameters was observed after seven weeks of exposure in individuals exposed to higher concentrations of ND (200 μg g−1 food). In animals exposed to lower concentrations of ND (20 μg g−1 food), there were few significant changes to these parameters. Analysis of DNA damage performed after fourteen weeks using the comet assay revealed DNA instabilities in the insects, especially the ones that had been exposed to the higher doses of ND. These findings may suggest that the toxicity of ND is concentration dependent. While high doses interact in a toxic manner, trace amounts, which are more likely in the environment, might be safe for organisms. Extreme caution should be taken when handling nanodiamonds.