Animals are expected to choose foods that optimize their growth, reproduction and survival, but it remains unclear how environmental stressors modulate their dietary preference. Here, we provide the first report of nematode stress resulting from exposure to earthworm-produced cyclic peptides, and confirm that this stress changed the dietary choice of the model animal Caenorhabditis elegans and other soil-dwelling bacterial-feeding nematodes. Nematodes shift their food preference from preferred toward unpreferred bacteria when they are stressed by the toxic cyclic peptides. Furthermore, nematodes that eat more unpreferred bacteria are able to reallocate energy to repair cyclic peptide-induced damage of their DNA and complete their lifespan. Our results demonstrate that nematodes can actively change their dietary strategy to maintain survival at the cost of reproduction when they experience acute stress. This stress-driven adjustment of dietary choice in this predator-prey relationship may be the key to understand feeding ecology of predators in other food webs.