Reproduction and growth of Vallonia pulchella (O. F. Müller) and V. costata (O. F. Müller) were studied in laboratory conditions. Their ellipsoid and singly laid eggs are among the smallest heavily calcified (mean size 0.68×0.67×0.52 and 0.69×0.67×0.54 mm in V. pulchella and V. costata, respectively). V. pulchella reached morphological maturity (lip completion) at 3.25–3.50 whorls (mean 3.35), 49 to 166 days after hatching (85). The first egg (sexual maturity) was laid at 3.25–3.50 whorls (3.35), 50–283 days after hatching (162). The life span ranged from 628 to 940 days (779), the time elapsing between the last egg and death was 12–184 days (111). In V. costata the lip was completed at 3.25–3.50 whorls (3.37), 42 to 183 days after hatching (120). The first egg was laid at 3.25–3.50 whorls (3.42), 131–290 days after hatching (193). The life span ranged from 360 to 841 days (709) and the time elapsing between the last egg and death was 11–692 days (210). The egg production rate and juvenile life span in individuals kept in isolation were the same as in those kept in pairs or larger groups. The growth pattern was similar in the two species: fast phase followed by slow phase. However, the formation of ribs on the shell surface of V. costata probably slowed down its growth rate. The life history traits shared by the two Vallonia species are determined growth, iteroparity, longevity and predominantly selfing reproductive mode. The greater lifetime fecundity, shorter incubation period, faster growth and longer life span predestine V. pulchella to be a better coloniser than V. costata.