Bombyx mori silk only once annually. The second type is called bivoltine and is normally found in China, Japan, and Korea. The breeding process of this type takes place twice annually, a feat made possible through the slightly warmer climates and the resulting two life cycles. The polyvoltine type of mulberry silkworm can only be found in the tropics. The eggs are laid by female moths and hatch within nine to 12 days, so the resulting type can have up to eight separate life cycles throughout the year. Eggs take about 14 days to hatch into larvae, which eat continuously. They have
Bombyx mandarina true or mulberry silkmoths. The origin of the domesticated silkmoth is enigmatic. It has been suggested that it is the survivor of an extinct species which diverged from the ancestors of "Bombyx mandarina" millions of years ago. However, this is based on an untenable molecular clock hypothesis that assumes that wild and domestic silkmoths evolved equally fast after their lineages diverged. Rather, the effects of artificial selection have accelerated evolution in the domestic form to a point where it is hard to trace the origin of the numerous breeds of domestic silkworms even with the most modern molecular phylogeny methods.