The iris is pollinated by the accurately named “long-proboscid fly”, whose tongue is twice as long as its body. It hovers over the flower and aims for the centre, driving its tongue deep into the stem to reach the pool of nectar at the bottom. As it drinks, its head pushes against the flower’s male organs, which deposit a dollop of pollen. When the fly leaves, it carries this payload to another iris. The flies and the flowers are intimate partners of evolution. The long tongues and stems have been perfectly aligned to give one partner a drink and the other a flying sexual aide.
All of this depends on the white arrows. When Dennis Hansen from the University of Kwazulu-Natal painted over the markings, the fly could no longer find the flower’s centre. The arrows are like a sign that says, “Insert tongue here”.