Bees are oblivious to the huge pollination service they perform. Pollen is bees’ sole dietary source of protein. They absolutely require pollen from a variety of plants to feed to their offspring (larvae). The protein level in pollen from different plant sources ranges from 2.5 to 60 percent, and bees prefer pollens with high protein levels. Pollen also contains some lipids, sterols, vitamins, minerals, and carbohydrates.Wind-pollinated plants like corn, which span thousands of acres across the US, produce lots of pollen. But corn pollen to bees is somewhat equivalent to corn cobs to humans: bland fiber. If starved, or if corn pollen is the only source of protein around, bees will collect it. Grass pollen, like corn, is of low nutritional value to bees and is generally avoided by them.Bees also visit flowers for another dietary reward produced by the plant: nectar. Nectar is a sugary plant secretion that also contains trace amounts of amino acids, proteins, lipids, and vitamins. It is bees’ main dietary source of carbohydrates.

The Evolution Of Bee Flowers

Flowers that require cross-pollination have evolved fascinating and beautiful ways to lure bees and other animals into collecting their pollen.

From a bee’s perspective, these evolved traits are classified by four characteristics: 1. whether flowers have color patterns and aromas that are attractive; 2. whether the pollen can be readily released from the anther; 3. whether the protein content in the pollen is high enough to meet the bee’s nutritional needs, and; 4. whether there is a nectar reward hidden in the flower.

Simply put, flowers that do not require cross-pollination are not attractive to bees. Humans have bred some flowers, such as tulips or daffodils, to be highly attractive to other humans, but bees have a different palette; a flower can look attractive to a bee, but if it doesn’t yield high-quality pollen or have a nectar reward, it is just background decoration, not worthy of attention.

Specifically, the flowers that are attractive to bees have evolved odors that are sweet and light. They have evolved color patterns that fall within the visual range of bees. Bees are not sensitive to light in the red spectrum, but they are sensitive to wavelengths in the ultraviolet spectrum. Some flowers have patches of color that contain ultraviolet reflectance that bees can see but humans cannot. Often these UV patches are arranged like landing lights, or nectar guides, on the petals, directing the bee into the rewarding reproductive parts of the flower. The color patterns of flowers also provide cues to passing bees about the quality and quantity of a flower’s nectar.

The wells that secrete nectar, called nectaries, are strategically placed at the base of the reproductive structures of the flower. As a hungry bee reaches its tongue, or proboscis, into the nectary for some carbohydrate energy, the bee inadvertently deposits pollen collected from a previous flower she visited, resulting in pollination. The bee is rewarded with nectar, and the flower is rewarded with a little pollen that rubs off the bee. It’s a win-win situation for both.