Solitary bees are often ignored in favour of their honey-producing brethren but their incredible importance as pollinators cannot be overestimated
We all know honeybees, and the majority of us are equally familiar with bumblebees, even if we struggle to name them individually, but solitary bees? They are a huge group that most of us know little about but of the 270 species of bee found in Britain, nearly 250 of them are what are known as solitary bees. If that sounds a lot, some 20,000 bee species have been described worldwide, and there are surely many more yet to be named. For the record, there are 24 species of bumblebees to be found in these isles, along with the single species of honeybee.
Few of the solitary bees have English names, while specific identification is usually a challenge even for experts. A small number are easy to name but for most a microscope is needed: the submarginal cells on the forewing are of great value in specific identification, as is the form of the tongue. It’s a highly complicated business and explains why so few have anything other than a scientific name.
Solitary bees make up a huge group
Solitary bees are aptly named, as they don’t live in colonies like honeybees or most bumblebees. None use hives, while more than half of them nest in the ground, where they excavate their own chamber. However, the solitary bees are a remarkably diverse and varied lot, so quite a number of them play by a different set of rules. Some build so-called ‘aerial nests’, typically taking over old beetle holes in vegetation. We also have one species of solitary bee, a small metallic-blue insect called Ceratina cyanea, that excavates its own aerial nest, usually in bramble stems. It digs out the pith of the stem to create the space to lay its eggs. There is also a trio of snail-shell-nesting bees, using empty shells for their nests – a remarkably sensible arrangement.
Though there are several families of solitary bees, they all feed on pollen and nectar, making them incredibly important pollinators in the countryside, to the benefit of natural ecosystems and the agricultural economy. While honeybees tend to get all the credit for pollinating plants, studies have shown that solitary bees are two or three times as effective as pollinators. There’s a simple reason for this. Pollen often sticks to a bee when it has visited a flower. This is usually carried back to the hive by a honeybee but solitary bees will visit many more flowers, thus becoming pollen spreaders. They also require less pollen as a food source as they don’t live in hives.
Often ignored despite their important pollinating role
Despite their importance as pollinators, solitary bees tend to be ignored and their value never fully appreciated. Studies of these bees are relatively few but we do know that numbers have declined dramatically in recent decades, for all the usual reasons. Climate change is one factor, as is increased pesticide use, but habitat change is almost certainly the greatest problem. Converting natural habitats into agricultural landscapes is bound to have a major impact on insects that depend on a rich floral diversity for their survival. Large monocultures cannot support populations of wild bees.
I have a neighbour who, concerned about the health of the soil on his 1,000-acre farm, has turned to regenerative agriculture. He joined me when I undertook a GWCT Big Farmland Bird Count on his farm, explaining to me that what he called “cides” – that’s pesticides and herbicides – are cheap, so farmers are encouraged to use them even if they haven’t got a problem. “The argument goes that you might just as well use them, as a sort of insurance, as if you don’t you might find you have an infestation of aphids or whatever,” he said. “If pesticides were three or four times the price, then they would be used much more selectively.”
Pesticides and herbicides used too liberally
He went on to tell me that he has decided not to grow sugar beet any more for a number of reasons. One is the damage harvesting the beet does to his light soil, but a major consideration is the use of neonicotinoid seed treatments on sugar beet seed to control aphids, particularly the peach potato aphid. Curiously, the aphids themselves are not a significant problem but they spread viruses including beet yellows virus, beet chlorosis virus and beet mild yellowing virus. In 2023 the Government has once again authorised “the limited and controlled use” of the product Cruiser SB, which contains the neonicotinoid thiamethoxam, for the treatment of sugar beet seed. Neonics, as they are generally known, are exceedingly dangerous to bees, with wild bees particularly vulnerable.
To protect solitary bees it’s vital to make as many people as possible aware of their existence, not to mention their importance. There are a number of solitary bees that are relatively easy to identify, with the mining bees perhaps the simplest. There are 65 species of mining bees belonging to the genus Andrena, making this the largest bee genus in Britain. They are highly variable in size, with the smallest just 5mm long and the largest more than three times that length. Their name comes from the fact that they all nest in the soil. These bees have short pointed tongues and are characterised by the grooves running down the inside of their eyes. They all collect pollen on their hind legs.
Easily identified solitary bees
Several of the mining bees have English names, reflecting the fact that they are relatively easy to see and identify. A classic example is the tawny mining bee, a common, spring-flying bee that you might well find nesting in your lawn. Here it produces little mounds of soil, resembling miniature volcanoes, around the mouth of its burrow. The bees themselves are bright ginger; females are bigger than males, while the latter have distinguishing white hairs on their face.
Another distinctive species is the wool carder bee, a leaf-cutting or mason bee. It’s an attractive, robust, bicoloured insect that collects hairs from plants to build its nest, behaviour that was first noted by the naturalist Gilbert White in his garden at Selborne in the mid-18th century. Males are twice the size of the females and are highly territorial: watch carefully and you will see them defending a patch of flowers for their mate to forage in. They don’t have stings but they will wrestle any insect that invades their territory, even crushing intruders to death. Most common in southern England, this species is on the wing from May to August.
Mason bees are a common sight around old buildings
Perhaps the best known of all the solitary bees is the red mason bee, a small, common insect that likes to nest in the crumbling mortar of old buildings, though it will use hollow plant stems or even holes in cliffs. On the wing from late March, this species is often found in urban environments, particularly favouring gardens and parks. Look for them feeding on spring-flowering shrubs and trees, especially apples and pears. This bee is exceptionally important for pollinating orchards, while it is also attracted to oilseed rape fields.
The red mason is a fairly easy species to recognise. Note the box-shaped head with distinctive inward curved horns on the top, a feature not found in any other British species. Red masons have brown-haired thoraxes and orange-haired abdomens. The females collect pollen in these orange hairs in a structure known as a pollen brush. Depending on the colour of the pollen, it can make the bee’s underside look unexpectedly bright.
Watch how bees move to identify them
Birdwatchers talk about identifying birds by their jizz; the distinctive way that they move. With a little practice you can do the same with bees. The hairy-footed flower bee is one of the first solitary bees to emerge in spring and is easily confused with a small bumblebee. But while bumblebees have a bumbling flight, hairy-foots have a distinctive quick, darting flight action – a good way to pick them out. Like a number of solitary bees, this species exhibits strong sexual dimorphism, with the males and females looking quite different. The former are gingery brown, while the females are all black, except for distinctive orange hairs on their rear legs. Although solitary by name they often nest in large and noisy groups.
All solitary bees depend on nectar to survive, so the best way we can help them is by planting nectar mixtures in our gardens or on our farms. Vetch, clovers, lucerne, ox-eye daisies, knapweed and bird’s-foot trefoil will all be appreciated by our solitary bees, along with the more obvious bumblebees and butterflies. Such mixes add a vibrant splash of colour to the countryside, but they add a vital lifeline to a group of insects on which we, perhaps unknowingly, depend.
How to make a bee hotel
Bee hotels can be bought at a modest price from garden centres, manufacturers of bird boxes and charities but they are easy to make. A good starting-point is a wooden box without a front. If the box is small there’s no need to compartmentalise it, but a larger box will benefit from being divided into sections. Pack each one with hollow plants or reeds – the greater variety of size, the better. All should be cut to the depth of the box. In addition to the hollow stems, wooden blocks drilled with deep holes of varying sizes can be included. Siting the box is crucial: solitary bees like warmth and sunshine, so ensure it is south-facing and close to bee-friendly flowers and shrubs. It can be anything up to six feet from the ground and should be fixed so it doesn’t move around. Evidence that holes have been used will be the end plugged with leaves or mud. The bee grubs will overwinter in the box, emerging the following spring.
Want to learn more about helping wildlife?
If you enjoyed this feature, check out more of the The Field‘s conservation content. Click here to read our article about rewilding and here to learn how to plant a garden to help insects.