The passion flowers have a unique structure, which in most cases requires a large bee to effectively pollinate. In the American tropics, wooden beams are mounted very near passionfruit plantings to encourage carpenter bees to nest. The size and structure of flowers of other Passiflora species is optimized for pollination by hummingbirds (especially hermits like Phaethornis), bumble bees, wasps or bats, while yet others are self-pollinating. The Sword-billed Hummingbird (Ensifera ensifera) with its immensely elongated bill has co-evolved with certain passion flowers, such as P. mixta.
Yellow Passion Flower (P. lutea) pollen is apparently the only pollen eaten by the unusual bee Anthemurgus passiflorae. However, these bees simply collect the pollen, but do not pollinate the flowers.
The leaves are used as food plants by the larva of a number of lepidoptera. To prevent the butterflies from laying too many eggs on any single plant, some passion flowers bear small colored nubs which resemble the butterflies' eggs and seem to fool them into believing that more eggs have already been deposited on a plant than actually is the case. Also, many Passiflora species produce sweet nutrient-rich liquid from glands on their leaf stems. These fluids attract ants which will kill and eat many pests that they happen to find feeding on the passion flowers. Lepidoptera larvae are known to feed on the following.
The Passion fruit or maracujá (P. edulis) is cultivated extensively in the Caribbean and south Florida and South Africa for its fruit, which is used as a source of juice. A small purple fruit which wrinkles easily and a larger shiny yellow to orange fruit are traded under this name. The latter is usually considered just a variety flavicarpa, but seems to be more distinct in fact.