Even though only comparably scanty data are available on karyotypes and chromosome structure of stick insects, it is known that there are different sex chromosome systems in Phasmatodea. Most stick insects have, besides numerous autosomes, only one gonosome—i.e., one X chromosome. This X0-system is most likely the ancestral sex chromosome system (68 taxa, present in 36 of 46 studied genera). The second largest group of Phasmatodea species exhibits an XY sex chromosome system (13 species, eight genera) . Additionally, Didymuria violescens has males with both X0 and XY complements. Out of 95 studied bisexual species, nine were found with XX/XY, while in the others an XX/X0 sex chromosome system was observed .