Many plants have coevolved with other organisms (pollinators) to such an extent that the main or only means the plant has of transporting the male elements (pollen) to the female element (ovule) to assure reproduction is through the intersession of the pollinator. And the same time, many pollinators have become dependent on the nectar and pollen produced by plants for their nutrition. It has been calculated that without pollinators a third of flowering plants would produce no seed and half of all flowering plants would have their fertility reduced by 80%. Pollinators are estimated to contribute 24 billion dollars each year to the US economy by making possible the reproduction of plants of economic importance. The phenomenon of pollination is an active area of research in disciplines such as ecology and evolutionary biology.
In the video bellow an Eastern Tiger Swallowtail butterfly (Papilio glaucus) feasts on the nectar of the flower of a thistle plant promoting its reproduction in the process.