Pollinators visit flowers primarily to eat. Nectar and pollen are the two main food rewards that drive the vast majority of flower visits, supplying sugars for quick energy and protein for growth and reproduction. But food is only part of the story. Flowers also offer warmth, building materials, mating sites, and even shelter for raising young, and some flowers trick pollinators into visiting without offering any reward at all.
Nectar: The Main Energy Source
Nectar is a sugar solution produced by glands inside (and sometimes outside) the flower. It contains three main sugars: sucrose, glucose, and fructose. For pollinators, it functions like a high-energy drink that fuels flight and daily activity. The sugar concentration varies widely depending on the plant. Canola nectar ranges from 29% to 84% sugar, while citrus flowers produce nectar at a more modest 23% to 37%.
Different pollinators prefer different concentrations. Honeybees, bumblebees, and stingless bees gravitate toward nectar in the 50% to 65% sugar range, which is thick and energy-dense. Orchid bees, by contrast, sip nectar through a proboscis rather than lapping it up, so they get the fastest energy intake from thinner nectar around 30% to 40%. Butterflies and moths, which also feed through a tube-like mouthpart, tend to favor similarly dilute nectar. These preferences mean that a flower’s sugar concentration partly determines which pollinators show up.
Pollen: Protein for Reproduction
While nectar powers flight, pollen feeds the next generation. Bees collect pollen to bring back to their nests, where it serves as the primary protein and fat source for developing larvae. Pollen protein content varies enormously, from as low as 1.5% to nearly 50%, and lipid (fat) content ranges from about 1% to 25%. These aren’t random numbers. The ratio of protein to lipid in pollen appears to influence which bee species collect from which flowers.
Plants in the legume family (Fabaceae) produce pollen with a high protein-to-lipid ratio, around 3.8 to 1. Daisy-family plants (Asteraceae) sit at nearly 1 to 1, meaning roughly equal protein and fat. Bumblebees tend to collect from plants with higher protein-to-lipid ratios, which aligns with their greater protein needs for raising large colonies in cool climates. Solitary bees like the horn-faced bee collect pollen closer to a 2.9 to 1 ratio. So when a bumblebee bypasses one flower for another, it may be selecting for nutritional quality, not just convenience.
How Flowers Advertise Their Rewards
Flowers don’t passively wait to be discovered. They actively signal to pollinators through color, pattern, and scent, and these signals are tuned to the sensory abilities of specific visitors.
Color and Ultraviolet Patterns
Many flowers carry patterns visible only in ultraviolet light, which bees and many other insects can see but humans cannot. These “nectar guides” are lines, spots, or markings that point directly toward the nectar source inside the flower. In experiments with a lily species pollinated by flies, removing the arrow-shaped markings on petals dramatically reduced the chance that a visiting fly could actually insert its mouthpart and reach the nectar. Flies approached the altered flowers at similar rates but hovered above the opening, unable to find their way in. When all six petal markings were present, flies probed successfully almost every time.
Flower color also targets specific pollinators. Bee-pollinated flowers tend to be bright white, yellow, blue, or UV-reflective. Bird-pollinated flowers lean toward scarlet, orange, and red, colors that birds see well but bees largely ignore. Bat-pollinated flowers are often dull white, green, or purple, and open at night when their visitors are active. Butterfly flowers are bright and often include red and purple tones, with wide landing platforms and narrow tubes that match a butterfly’s long proboscis.
Scent
Floral scent is a cocktail of volatile organic compounds, mainly terpenes and benzenoid aromatics, along with smaller amounts of alcohols, esters, and fatty acid derivatives. Different compound blends attract different pollinators. Night-blooming flowers pollinated by moths often produce heavy, sweet fragrances that carry well in still evening air. Flowers targeting beetles may smell fruity or fermented. The specificity can be remarkable: some orchids produce a single compound found nowhere else in the plant kingdom, tuned to attract one species of insect.
Rewards Beyond Food
Not every pollinator visits a flower for a meal. Some come for warmth. Thermogenic plants, found in families like Magnoliaceae, produce significant heat during blooming, keeping their flower chambers warmer than the surrounding air. For beetles that shelter inside these flowers overnight, the warmth is a direct energy savings. They burn fewer calories staying warm, which in cool environments is a meaningful benefit. The plant gets pollinated; the beetle gets a heated room.
Other flowers offer oils or resins that certain bees collect for nest construction rather than food. Some tropical plants in the genus Dalechampia, for example, produce floral resins that bees use to waterproof and reinforce their nests. Still other flowers function as mating sites. Enclosed chambers formed by floral bracts provide shelter from predators and a reliable place for insects to find mates. In brood-site pollination systems, plants go even further, providing a place for insects to lay eggs and for larvae to develop. The plant essentially trades nursery space for pollination services.
When Flowers Cheat
Some plants, particularly orchids, lure pollinators without offering any reward. The most striking strategy is sexual deception. Certain orchids produce chemicals that precisely mimic the sex pheromones of female wasps. Male wasps land on the flower and attempt to mate with it, picking up pollen in the process. One Australian orchid, Caladenia plicata, achieves this by producing two compounds from completely independent chemical pathways. Blended at a 1 to 4 ratio, these compounds trigger attempted mating in about 70% of male thynnine wasps that encounter them, a rate equivalent to what happens at real orchid flowers in the wild.
Other deceptive flowers mimic the appearance of rewarding species without producing nectar. A pollinator that has learned to associate a certain color or shape with food visits the mimic, finds nothing, and leaves, but not before transferring pollen. These strategies work only when the deceptive species is relatively rare compared to the genuine food sources nearby. If too many flowers cheat, pollinators learn to avoid them.
Why This Relationship Matters
The exchange between flowers and pollinators underpins a large portion of global food production. According to the Food and Agriculture Organization of the United Nations, pollinator services to crops are worth more than $235 billion per year. About 75% of leading food crops depend to some degree on animal pollination, including fruits, vegetables, nuts, and oilseeds. The relationship is not charity on either side. Flowers invest significant metabolic resources in producing nectar, pollen, scent, and color. Pollinators spend energy flying between blooms and risk predation while foraging. Both sides benefit only when the exchange works, which is why flowers have evolved such precise ways to attract the right visitor and why pollinators have developed equally precise abilities to find and evaluate the best rewards.