花蜜是开花植物的花内蜜腺等分泌的一种主要成分是小分子糖类、比如双糖的蔗糖、单糖的果糖、葡萄糖及半乳糖、甚或三糖棉子糖，四糖水苏糖等的混和物，其种类与比例会随物种甚或品种有相当变化。可吸引授粉昆虫来采蜜，从而达到帮助授粉的目的。蜜蜂采集花蜜可酿成蜂蜜。

花蜜的浓度会随环境而变化，比如椴树在空气湿度为51%时，花蜜含糖量为72%；湿度为100%时，含糖量只有22%。蜜蜂喜欢采食含糖高的花蜜。

然而部分花蜜与花粉对蜜蜂具有毒性，比如含有半乳糖的茶花，以及钾离子含量偏高的枣花；甚或对人具有毒性，比如雷公藤（Tripterygium wilfordii Hook.F.）、博落回 （Macleaya cordata (Willd.) R.Br）、狼毒（Stellera chamaejasme L.）。

Nectar is a sugar-rich liquid produced by plants in glands called nectaries, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide antiherbivore protection. Common nectar-consuming pollinators include bees, butterflies and moths, hummingbirds, and bats. Nectar plays an important role in the foraging economics and overall evolution of nectar-eating species; for example, nectar and its properties are responsible for the differential evolution of the African honey bee, A. m. scutellata and the western honey bee.