As many snails, individuals of L. cyclindracea are hermaphrodites, which mate with each other to fertilize their eggs. This species, however, is relatively unusual for a snail in that it is ovoviviparous. It retains its eggs - 4 to 6 -inside its body until they hatch, and they are born into miniature snails, even tinier than their parents. Some of these juveniles were also present under the shell near the adults. The snails reach maturity at two years old and can live over 5 years, reaching a maximum size of a mighty 3.5 mm.
Active hatchlings are advantageous, as compared to eggs, in that they can immediately start to feed, grow, fight off fungi, cope with brief periods of desiccation by moving into deeper layers of litter or temporarily retreating into their shell, and avoid drowning (or being washed away) as a result of occasional flooding of the riparian litter habitat, by moving into higher layers.They compared this reproductive strategy in minute snails with the situation in larger species:
Large snails can produce eggs in vast numbers. Further, lack of size constraints enables the large adult to lay large eggs, generously coated with thick layers of albumin and mucus to tide the developing embryos over varying periods of drought and hunger. In Helix texfa, a species of 40 mm and 4.3 g (found in Israel very close to our present study site), each single egg averages 5.5 mm in size and 70 mg in wet weight (bigger and heavier than an entire adult Lauria), an adult produces 60 eggs per clutch, and clutch weight represents about 10% of body weight (Heller & Ittiel, 1990). In large snails with large clutches also sib cannibalism may occur, thereby increasing survival chances of the first individual to hatch (Baur, 1994). Further, large oviparous snails frequently deposit their eggs into pockets in moist soil. A deep cavity lined with mucus can protect the eggs against bacteria and fungi (Baur, 1994); it also enables the deposition of eggs in soil layers that remain damp for longer periods of time, and thereby reduces risks of desiccation. The cavity is dug out by the snail’s foot, so its depth is broadly correlated to foot size. Helix can dig 5cm into moist soil and Arclzachatina can dig a 15 cm cavity in one night (Tompa, 1984; Baur, 1994). Minute snails, however, do not have the potential to dig much beyond 0.2cm (except for subterranean genera, see Heller, Pimstein & Vaginsky, 1991). They can either dig minute cavities, or deposit their eggs in damp litter, where they would be exposed to fungi. Ovoviviparity may thus be a mode of parental care for snails that can neither lay many eggs, nor big eggs, nor dig deep egg cavities.I will keep looking for these snails to see how widespread they are in the garden. I wouldn't be surprised to have overlooked these fascinating creatures due to their minute size. Were not for the white background of the shell where we found them we would have probably missed them altogether.
Heller, J., Sivan, N. & Hodgson, A. (1997). Reproductive biology and population dynamics of an ovoviviparous land snail (Pupillidae). Journal of Zoology, 243 (2), 263-280 DOI: 10.1111/j.1469-7998.1997.tb02781.x