1. A pulmonate land snail, Fruticicola (Acusta) sieboldiana (Pfeiffer), which is a pest of vegetables in Japan, shows daily rhythmic activity. During daytime it rests beneath the soil surface or on various materials in the shade, and begins to move after the sunset when illumination intensity reduces to 0 lux, and 2 hours later activity reaches the maximum state. After that time active individuals gradually fall down and scarcely move about after the sunrise. 2. Light seems to be the most important factor in controlling the activity. 3. Fine weather or dryness inhibits the activity, but rainfall accelerates it. Temperature, within the normal daily march, seems to be less important. 4. No biotic factors seem to have important influences on the activity.

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