A lot is written about how important dandelions (Taraxacum officinale) are to the honey bee. Indeed, honey bees flock to dandelions both in the early spring and in times of dearth when little else is in bloom. But unlike some other pollen plants, dandelions are only a mediocre food source.
The problem, it seems, is that dandelions are missing some of the amino acids needed to manufacture protein. You can think of amino acids like letters in the alphabet–you need all 26 letters if you’re going to form all the words. Likewise, a bee needs a full complement of the necessary amino acids if it is going to make all the proteins it needs to raise young bees.
Of the set of amino acids that bees need, dandelion pollen falls short of four: arginine, isoleucine, leucine, and valine. Researchers have found that honey bees fed dandelion pollen alone have low success at raising brood. In fact, some researchers found that that honey bees fail to raise any brood when fed dandelion pollen alone.
Remember, dandelion pollen is not toxic, it’s just not complete. Potatoes are not toxic either, but if you ate only potatoes you’d be missing important parts of your diet.
Bees, like humans, need a varied diet from a number of sources to be healthy. The dandelion problem is a good example of what can happen if bees are fed a single pollen (monoculture) diet. Although some pollens are better sources than others, the best thing for the bees (or us) is to eat a wide variety of foods.