Dormancy in the land snail, Helicella virgata (Pulminata : Helicidae)

Abstract

H. virgata and other introduced snails of the family Helicidae spend much of their time in a dormant state. In winter, dormancy usually occurs daily, and lasts for a few hours only. In summer, when rainfall is rare, it may last for many days or even weeks, and is then referred to as aestivation. H. virgata aestivates in conspicuous positions, often fully exposed to the sun, at heights of up to 11 m from the ground. No appreciable heat is lost by evaporative cooling, and the temperatures of dormant snails may exceed the ambient temperature by as much as 10 degC, the amount of the excess being a function of height above the ground. Estimates are given of the temperatures experienced by aestivating snails over a whole summer; these exceed 30°C for three-quarters of the summer, and 40°C is reached quite commonly. The positions where H. virgata aestivate are discussed in relation to temperature, and it is concluded that their behaviour, which presumably evolved in their native European range, is less appropriate in the climate of South Australia; but despite this, their populations reach high densities in places.