Temperature can be a limiting factor on parasite development. Riccardoella limacum, a haematophagous mite, lives in the mantle cavity of helicid land snails. The prevalence of infection by R. limacum in populations of the land snail Arianta arbustorum is highly variable (0–78%) in Switzerland. However, parasitic mites do not occur in host populations at altitudes of 1290 m or higher. It has been hypothesized that the host's hibernation period might be too long at high elevations for mites and their eggs to survive. To test this hypothesis, we experimentally infected snails and allowed them to hibernate at 4°C for periods of 4–7 months. Winter survival of host snails was negatively affected by R. limacum. The intensity of mite infection decreased with increasing hibernation duration. Another experiment with shorter recording intervals revealed that mites do not leave the host when it buries in the soil at the beginning of hibernation. The number of mites decreased after 24 days of hibernation, whereas the number of eggs attached to the lung tissue remained constant throughout hibernation. Thus, R. limacum survives the winter in the egg stage in the host. Low temperature at high altitudes may limit the occurrence of R. limacum.

The route of transmission and host finding behaviour are fundamental components of a parasite's fitness. Riccardoella limacum, a haematophagous mite, lives in the mantle cavity of helicid land snails. To date it has been assumed that this parasitic mite is transmitted during courtship and mating of the host. Here we present experimental evidence for a new transmission route in the host snail Arianta arbustorum. Parasite-free snails were kept on soil on which previously infected host snails had been maintained for 6 weeks. R. limacum was successfully transmitted via soil without physical contact among hosts in 10 out of 22 (45·5%) cases. In a series of experiments we also examined the off-host locomotion of R. limacum on snail mucus and control substrates using an automated camera system. Parasitic mites showed a preference to move on fresh mucus. Our results support the hypothesis that R. limacum uses mucus trails to locate new hosts. These findings should be considered in commercial snail farming and when examining the epidemiology of wild populations.

Many simultaneously hermaphroditic land snails have sperm digesting glands and multiple sperm storage organs, which it is suggested give the sperm recipient control over the number of sperm accepted and hence fertilization. In order to increase fertilization success, the sperm donor should manipulate the recipient to accept more sperm, especially so in situations of sperm competition. In helicid snails, the love dart optionally pushed into the partner's body during courtship, has been suggested to be such a manipulative tool. We investigated the influence of the sperm donor's size, sperm volume transferred and dart pushing on the volume of allosperm stored by the recipient in virgin Arianta arbustorum. In addition, we were interested in sperm storage patterns within the spermathecae. Fifty per cent of the snails already possessed a dart and tried to use it. However, most of them missed the partner. The main tubule always contained more than 50% of the total amount of sperm stored. Otherwise sperm storage patterns were very variable. The volume of sperm stored was significantly influenced only by the number of spermathecal tubules. The significance of spermathecal morphology for sperm storage needs further exploration.

The morphology of the sperm storage organ (spermatheca) may influence the outcome of sperm competition in a variety of invertebrate species. Simultaneously hermaphroditic pulmonates show considerable inter- and intraspecific variation in the structure of the spermatheca. The morphological variation in the spermatheca (number of spermathecal tubules and tubule length) and the amount of sperm stored in the tubules in 115 individuals of the simultaneously hermaphroditic land snail Arianta arbustorum (L.) from six natural populations in the Eastern Alps (Gesäuse, Austria) was examined. The populations differed in snail density, therefore in the number of potential mating partners (range: 0.9–39.8 individuals/m2) and thus in the sperm competition risk. The number of spermathecal tubules ranged from two to nine. However, the six populations did not differ in either the mean number of spermathecal tubules, the length of the main tubule (range 0.9–3.4 mm), or in the cumulative length of the tubules (range 1.5–7.8 mm). The number of tubules and tubule length were not correlated with either shell height and shell breadth or with population density. The amount of sperm stored in the spermathecal tubules was estimated. Individuals from different populations did not differ in the amount of sperm stored, and the amount of sperm stored was not correlated with population density. Results indicate that the risk of sperm competition does not affect the complexity of the spermatheca (number of spermathecal tubules) in this snail. However, the possibility that individuals in high-density populations store sperm from more different mating partners than those in low-density populations remains to be examined.