Pollination is the process of transfer of pollen grains from anther to the stigma of the flower. Pollination does not guarantee the transfer of the right type of pollen. Many a times, pollen of the wrong type may land on the stigma of the flower. Although, the pistil of flower can identify the pollen of its own type (compatible) or not.

The pollen grain and nectar made by the plants are consumed by the insect visiting their flower without supporting in pollination. Such insects are referred to as nectar robbers or pollen robbers.

Many plants who have bisexual flowers have devices to avoid self-pollination. One such process or device is pollen release and stigma receptivity are not synchronised.