The taxon Forficula auricularia L. (Dermaptera: Forficulidae) is a complex of two sibling species that differ in life history (number of clutches per year and imaginal diapause) and that have diverged at the molecular level. The study of a contact zone in the Pyrenean Mountains, using the PCR-RFLP method on two mitochondrial regions (the 16S rRNA and the Cytochrome Oxidase intergenic region), revealed the coexistence of the sibling species at intermediate altitude (1200 m) whereas at lower and higher altitudes only one species was found. An allozyme study, conducted simultaneously and based on four polymorphic loci (PGI1, AAT1, Est-P1 and Est-P2), showed no sign of nuclear introgression. The apparent lack of hybridization in the field is consistent with a postzygotic barrier observed in the laboratory (a nearly complete failure to produce F1 hybrids). This contact zone is probably a sympatric zone between two genetically differentiated species.