Passion vine butterflies lay eggs on passion vine leaves because that’s what the caterpillar is going to eat. Mostly, a butterfly will lay one egg per leaf so some passion vines have developed yellow spots to try and convince butterflies that the leaves are already egg laden. I haven’t seen this strategy working too well.
Once a caterpillar emerges it will begin a life of voraciously eating passion vine leaves. There’s an early video game quality about this as the mouth chomps back and forth across the leaves, cutting one arc after another.
However, despite the presence of caterpillars, butterflies continue to lay eggs on the leaves. So what happens when a caterpillar comes across an egg? It makes no distinction and down goes the egg. So long cousin Billy!