Why Solitary Bees are Such Amazing Pollinators:

Leafcutter bee on Ragwort

The relationship between bees and flowering plants goes back to the early Cetaceous period, and different species of bee have, over 100 million years or so, developed a number of different physiological adaptations and behavioural traits to enable them to collect pollen.

Pollen carried by honeybees and bumblebees is visibly quite obvious. Both have become extremely adept at packing their pollen loads carefully, and neatly, into the smooth, widened pollen baskets (corbicula) situated on the sides of their hind legs. Once the pollen is packed in, very little is likely to fall off - and what does fall off is not viable anyway. With these bees, it is the pollen that sticks to their body hair that helps pollinate flowering plants.

Solitary bees are less fastidious. They collect pollen on 'scopa'; stiff, branched hairs, located on their legs, under their abdomens, or along the sides of their bodies. 

As the female solitary bee collects pollen, she packs it onto her scopa less carefully, and without the addition of saliva to moisten it. This means it is far more likely to fall off when the bee visits the next flower....which in turn means the next flower is more likely to be pollinated. 

Added to this, some solitary bees carry less pollen in each load, so they need to make many more trips back and forth from the flowers to their nests than do honeybees and bumblebees. These extra foraging trips mean that many more flowers get pollinated in the process.

Perhaps the easiest way to explain the difference between bees' various pollen collecting apparatus, is with photographs….  

Bombus terrestris (Buff-tailed bee) on Buddleia

Bumblebees and honeybees can carry up to 50% of their weight in pollen! 

You can see from this photograph of a Buff-Tailed worker bumblebee, how neatly she has packed the pollen, which she has moistened with saliva, into her pollen baskets. Honeybees do the same.

Most of this pollen will make its way back to the nest, where it will provide developing larvae with the protein they need to grow.


Halictus rubicundus female

Most ground nesting solitary bees collect pollen on scopa situated on their back legs, or along the sides of their abdomens 

This image shows the pollen collecting hairs of the ground nesting bee 'Halictus rubicundus' BEFORE pollen collection. Note how hairy her legs are. 

This is another photograph of the same bee, H. rubicundus. This time her leg scopa are laden with pollen which she is about to take into her nest beneath the ground. 

A large amount of this bee's pollen load will never make it back to her nest as it will have been lost as she visited other flowers en route.

Most cavity nesting solitary bees, like the Leafcutter bee pictured here, collect pollen on their abdominal scopa. This method of collecting pollen is extremely messy and is one of the reasons why some Mason bees (close relatives of the leafcutter) are around 100 times more efficient as pollinators than honeybees.

So, there you have it. Solitary bees are in fact the unsung heroes of the pollinating world!

N.B. There are a few solitary bees that, unusually, carry pollen back to their nests in their crops.

Bumblebees and honeybees are, of course, also wonderful pollinators, but in different ways and for different reasons. More about this another day….