Vestia gulo and V. turgida are iteroparous simultaneous hermaphrodites. In the wild they are active from April till October; they reproduce in the spring and summer (egg retention from May to August), and hibernate from November till March. Their gonads show the greatest activity in the spring and summer (maturation of oocytes, intensive vitellogenesis: March–May, numerous mature oocytes: May–July; production and maturation of spermatozoa: March–May; numerous packets of mature spermatozoa: May–October), which coincides with the reproductive season. The onset of reproduction is determined by the size of the pool of vitellogenic and mature oocytes; oocyte production starts in the summer of the previous vegetation season and lasts till next spring. Mature spermatozoa are present in the gonad from spring till autumn which indicates an ability to mate during the whole active period. During hibernation the gonads contain no spermatids, mature spermatozoa or advanced vitellogenic oocytes.