Desert Snails: Problems of Heat, Water and Food

ABSTRACT The major physiological problems of survival for desert snails were studied in mcterochila boisseri, a pulmonate snail common in desert areas in the Near East. In summer these snails can be found in a dormant state on the barren soil surface, fully exposed to the sun; in winter they become active during rainy periods, when they feed and reproduce. The lethal temperature of Sphincterochila is between 50 and 55 °C, depending on time of exposure. The temperature of the dormant animal within the shell, exposed to the sun on the soil surface in summer, does not reach a lethal level, although the temperature of the surrounding soil surface far exceeds this temperature. The rate of water loss from dormant snails, exposed in their natural habitat in summer, is about 0·5 mg per day per snail. This rate, if continued unchanged, would give a yearly loss of less than 200 mg. A 4 g specimen contains about 1400 mg water, and since the water loss during the cooler part of the year probably is reduced, several years should elapse before critical levels of water loss would be reached. In snails collected in summer the water content was not reduced, indicating no measurable depletion of water reserves during the hot season. The oxygen consumption of dormant snails varies with temperature (Q10 = 2·4). It is so low that the tissues could support the metabolic rate for several years, thus permitting continued dormancy even during periods of drought extending over more than i year.