Aestivation behaviour and thermal relations of the pulmonate Theba pisana in a semi-arid environment

1. 1.|The pulmonate Theba pisana has successfully colonised semi-arid coastal areas in South Africa. Summer aestivation occurs on exposed plant stems. 2. 2.|Upper thermal limits are 49°C for 20 min exposure; 44°C for 312 h. Climbing avoids these limits. Substrate and air temperatures decline and are less variable above the soil. 3. 3.|Snails select optimum aestivation heights in different vegetation types; settle in the coolest compass sectors; orientate shell mouth upwards and cluster to reduce heating. 4. 4.|Arousal is induced by high temperatures (allowing escape) or by equable combinations of low temperatures and high humidities.