A life longevity of Ixodes ricinus and I. persulcatus have been examined in laboratory conditions. It was found that specimens infected with borreliae live slightly longer than non-infected ones (difference is not reliable); females live 1.5 times longer than males; I. ricinus lives 2-4 times longer than I. persulcatus. It is suggested that I. persulcatus has a higher rate of metabolism than I. ricinus and that the latter species obtains an ability to survive after the last moult two winters and keep an activity in two summer seasons not counting the year of moulting.