I found a chrysalis of an Agraulis vanillae a couple weeks ago and took it home to watch it emerge. It turned into its adult stage today, so I released it (fortunately, it’s quite warm and sunny today) and wondered if there are specific places or structures that caterpillars like to pupate on.
Pretty much anywhere that the larva thinks is safe and there is enough space to emerge successfully.
Of course different species have varied pupation strategies, some only ever pupate on the host plant, whereas others almost always move away to pupate elsewhere. Also it is worth noting that this can vary with season, so larvae may behave differently at different times of year. For instance autumn larvae going into diapause may well pupate away from the host plant whereas earlier in the year most pupate on the plant.