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How do bees get a balanced diet if they only eat pollen and nectar?

A worker buff-tailed bumblebee (Bombus terrestris) on a sunflower head  - www.Alamy.com
A worker buff-tailed bumblebee (Bombus terrestris) on a sunflower head - www.Alamy.com

Bees rank highly in the affections of gardeners, right up there with birds, butterflies and hedgehogs. Bees are also unique among insects in their dependence on flowers –more or less everything needed to fuel adult bees and to grow new, young bees comes from pollen and nectar. So, not surprisingly, the quantities and qualities of food for bees provided by different flowers have been the subject of exhaustive research. So much so that you could be forgiven for thinking that there’s nothing left to discover.

But, of course, there is, as some Polish research published in the journal PLOS ONE demonstrates. The researchers began with the fact that young, growing honeybees, just like growing children, need a range of elements to build their bodies. Some, such as phosphorus, potassium and (especially) nitrogen are needed in large amounts. Others, such as copper, iron, zinc and magnesium are needed in much smaller amounts. For young bees, all these elements must come almost entirely from pollen; nectar is a great source of energy, but provides few other nutrients.

So, here’s the question: how do the ratios of these elements in the pollen of different flowers compare with the ratios required to make bees? Or to put that another way, do some pollen types represent more of a balanced diet than others?

Our knowledge of the elemental concentrations of the pollen of different plants is far from complete, and the little we do know is often based on a single study. Nevertheless, the answer to that question turns out to be a definite yes. The composition of the pollen of some plants is very unbalanced, for example sunflower pollen is very low in phosphorus. Clover, on the other hand, is almost perfectly balanced, and given that clover has long been known to provide protein-rich pollen, it looks like an even better bee food than we had previously thought. Other legumes that provide well-balanced pollen include gorse and broad bean.

The honey business does not help wild bees - Credit: iStockphoto
The honey business does not necessarily help wild bees Credit: iStockphoto

But don’t panic; it’s not necessary to grow only plants with nutritionally-balanced pollen, any more than every mouthful of your food needs to represent a balanced diet. Bees aren’t stupid, and they’re perfectly capable of putting together a decent diet by mixing pollen from different plants, provided they’re given plenty to choose from. Yet more reason, in case you needed one, to grow a wide range of different flowers, ideally from spring to autumn.

A surprising postscript to this research is that all pollen, without exception, is short of sodium, so no amount of pollen mixing can provide enough. There’s hardly any in nectar either, yet bees seem to manage to get enough of this element, so it must be coming from somewhere. Honeybees are known to drink seawater, and may even attempt to drink human tears and sweat. Failing that, the slightly unsavoury answer is that bees get sodium from “dirty water” containing decomposing organic matter, and also from urine and even (urgh) poo.