DNA methylation is an important epigenetic mark in many eukaryotes, but until now it has not been identified in nematodes. This study identified 5-methylcytosine (5mC) in the parasitic nematode Trichinella spiralis using MethylC-seq to generate high-resolution methylome maps. The authors found substantial changes in 5mC between life-cycle stages, both in terms of overall levels and changes at specific genes. Given that the genome of the model nematode Caenorhabditis elegans does not contain 5mC, these findings raise evolutionary questions about the regulation of gene expression in related species.