Passion flowers grow in South America. They are so-called because they once reminded Catholic priests of Christ's passion (suffering and death). The flower's petals and sepals resembled the ten apostles and the circle of hair-like rays suggested Christ's crown of thorns.
The Heliconius butterfly lays its eggs on passion flower vines. When the caterpillars hatch, they have a ravenous appetite and can easily strip a healthy vine within days. Female Heliconius butterflies will not lay eggs on a plant which already has a batch. They instinctively know the vine will be unable to feed more than one hungry brood.
To protect itself, the passion flower develops a mass of tiny protusions that resemble butterfly eggs, either at the base of the leaves, or on the underside.