Many butterfly and moth caterpillars deliberately wander off of their host plant when ready to pupate. This helps them avoid detection by their predators, since they are fairly helpless as a pupa/chrysalis. Predators can "smell" plant injury (from the caterpillar chewing), see frass (droppings), or pick up on other cues that help them locate prey to eat or parasitize. By finding another location to pupate, the caterpillars lower the risk of discovery. It's not uncommon for Monarch caterpillars to form a chrysalis many feet from the plants they were feeding on. We do not recommend moving caterpillars into an enclosure, since it's best for their health to receive natural cues from the weather, the host plant, and daylength to stay "on track" for proper migration stimulation; plus, captive rearing might increase the risk of disease transmission from one larva to another.

Miri