Interestingly, we found that a long genomic region is required to regulate yellow gene expression in B. mori, whereas CREs are usually restricted to ~500–2000 bp in other insect species (eg D. melanogaster, T. castaneum, A. gambiae; Cande et al., 2009). Furthermore, as transcription factor binding sites are several tens of base pairs long, it is reasonable to assume that CREs would be a few hundred base pairs long as they are collections of binding sites (Spitz and Furlong, 2012). One possible reason for the apparently longer genomic region required to regulate yellow gene expression in B. mori could be the difference in genome size between B. mori and D. melanogaster: the genome of B. mori (482 Mb) is three times larger than that of D. melanogaster (175 Mb) [cf. T. castaneum (166 Mb) and A. gambiae (265 Mb)]. The numerous repetitive sequences (eg transposons) in the B. mori genome account, in part, for its large size (Mita et al., 2004; Osanai‐Futahashi et al., 2008), as has been observed in other lepidopterans (Papa et al., 2008). As previously suggested, numerous repetitive sequences may facilitate the extraordinary colour and pattern divergence seen in Lepidoptera.