Promoted by the barcoding approach, mitochondrial DNA is more than ever used as a molecular marker to distinguish and identify species. Yet, it has been repeatedly argued that it may be poorly suited for this purpose, especially in insects where mitochondria are often associated with invasive intracellular bacteria that may promote their introgression. Here we inform this debate by assessing how divergent nuclear genomes can be when mitochondrial barcodes indicate very high proximity. To this end, we obtained RAD-seq data from 92 barcode-based species-like units (that is Operational Taxonomic Units, OTU), spanning 4 insect orders. In 100% of the cases, the observed median nuclear divergence was lower than 2%, a value that was recently estimated as one below which nuclear gene flow is not uncommon. These results suggest that although mitochondria may occasionally leak between species, this process is rare enough in insects to make DNA barcoding a reliable tool for clustering specimens into species-like units.