Another valuable attribute of CAM plants is their capability for idling metabolism during droughts. The plant, however, maintains a low level of metabolism in the still-moist tissues. Just as an idling engine can rev up to full speed more quickly than a cold one, an idling CAM plant can resume full growth in 24 to 48 hours after a rain. Therefore, succulents can take rapid advantage of ephemeral surface moisture. Stored water in an arid environment requires protection from thirsty animals.
Most succulent plants are spiny or toxic, often both.
Some protect themselves by growing only in inaccessible locations. Still others rely on camouflage. Arizona night blooming cereus, for example, closely resembles the dry stems of the shrubs in which it grows. Plants in this category often shed leaves during dry periods and enter a deep dormancy. Most water loss is from transpiration through leaf surfaces, so dropping leaves conserves water in the stems.