Thus flowers must both attract and reward an insect visitor. The flower is shaped differently from the display of the leaves. The flower is usually a different color than leaves so that the flower is visible on the background of leaves. In general the coloration is designed so that the bee learns to distinguish it and associate a visit to that pattern with the reward. Flowers have evolved bull's-eye and nectar guide patterns in their floral displays to attract a passing bee into landing.
Some flowers also attract insect visitors with fragrances.
Bees have an excellent sense of smell with chemoreceptors in their antennae and are attracted to particular fragrances. The combination of visual and olfactory attractants gets the bee to land most frequently. The reward plants provide bees include nectar and pollen. The nectar is a sweet liquid composed of mostly sucrose. The bees collect this liquid in their crop.