A common relocation behavior by monarch caterpillars is performed by those of medium size : They spend the day either on stem near bottom, or off stem inside pot or on its outside, sometimes on something adjacent, Probably some are preparing to moult, but definitely not all, given that they commonly return to leaves in early evening. The following relocation behavior easily is observed among caterpillars in captivity together with others: Starting at an early age and continuing until very large, the smallest one or few depart the food, in deference to all larger. My practice of keeping them according to sizes in separate containers reduces the size-dictated fasting. Large caterpillars often will forage even when leaves are immediate. It normally is only in perceived scarcity that they strip a plant.

Caterpillar's appearance usually changes as they mature, early stages can be difficult to identify. Most caterpillars found at random will turn into moths, as they are far more common. So if you want butterflies, pass over any inchworms or loopers you find, caterpillars that make webs, fold leaves, etc.

Lisa, they may be preparing to molt, in which case they do tend to wander away from food and they stay immobilized for several hours (up to 24 or more sometimes). It is best not to bother them during this period of time. Don't worry, they will wander back onto food when they are ready to eat.

Susanne, you've got the Latin name turned around....it's Datana major. :-) These busy little pests turn into a rather plain brown moth, sodbuster. But regardless of that fact, if you value your azaleas, you had better get in there and remove those eating machines! They won't sting or bite, so just pick them off and fling them somewhere where your lazy birds can manage to find them.