1 Mar 2021

Solitary bees and where to see them

Ardd Fotaneg · Botanic Garden

My biggest passion is bees and their conservation, and I particularly love looking out for solitary bees when I’m out and about. I get very excited when I spot a species I haven’t seen before!

So what are solitary bees?

Solitary bees are called this because they don’t live in colonies like bumblebees and honey bees. Female solitary bees create and provision their nests alone, and therefore there is no cooperative brood care by worker bees. However, you may sometimes see solitary bees nesting in large aggregations. In a nest, there are separate cells that have been built by a mated female and each one contains pollen, nectar and a single egg. Cells containing females will be to the back of the nest row, and males will be at the front because males emerge before females. Solitary bee offspring develop without any further care from their mother after she has finished building her nest.

There are lots of different species of solitary bee in the UK, and they are split into different genera. Here is just a selection:

Mining bees (Andrena spp.)

Mining bees are ground-nesters, and they use loose soils so that they can successfully dig little burrows, often with side tunnels, which can be seen above ground as little mounds in the ground with a hole in the middle. They collect pollen to provision their nests on scopa, a pollen brush, which is situated on their hind legs.

There are many different species of mining bee, such as the Buffish Mining Bee (Andrena nigroaenea) and the Orange-tailed Mining Bee (Andrena haemorrhoa). One of the easiest to identify is the female Tawny Mining Bee (Andrena fulva). Her abdomen and thorax are a vibrant red/orange in colour, and her face is black, and she flies quite low to the ground. Males of this species are not as distinguishable as the females.

Mason bees (Osmia spp.)

Mason bees will nest in a variety of places where there are holes that they can use have already been established, such as in hollow plant stems, cavities in walls, bee hotels and even empty snail shells! In these holes, mated females will make nest cells and then block them up with mud, or masticated leaves, depending on the species.

Unlike mining bees, mason bees belong to the family Megachilidae, and so females collect pollen in a different way. They have a scopa under their abdomen which pollen collects on. If you watch one going in and out of her nest, you’ll see the change in colour of the underneath of her abdomen as she unloads the pollen into her cells.

A relatively widespread species that is quite recognisable is the Red Mason Bee (Osmia bicornis). Both males and females have ginger/brown hair, but the males are typically smaller than the females and look like they have a tiny moustache! They’re very cute! Females are frequently seen in bee hotels, so if you want to see them in your garden, making or buying a solitary bee hotel is definitely worthwhile.

Leafcutter bees (Megachile spp.)

Leafcutter bees are aerial nesters, which means that they nest above ground. They can nest in places like hollow stems, cavities in houses and solitary bee hotels. Mated females will cut pieces of leaves from plants, such as a rose, and then carry them back to her nest in her mandibles (jaws) to line and separate nest cells.

Like mason bees, leaf-cutter bees belong to the family Megachilidae, and so females collect pollen on a scopa under their abdomen and transport it to their nest.

A species of leaf-cutter bee that you might see in your garden is Willughby’s Leafcutter Bee (Megachile willughbiella). The males are particularly cute, as they have white, fluffy forelegs! You can often see males patrolling patches of flowers, such as bellflowers, for females.

Plasterer bees (Colletes spp.)

Plasterer bees are ground nesters, and they nest in loose soils so that they can dig burrows. Mated females line their nests with a substance that looks a lot like cellophane, and this acts as a water- and fungi-resistant coating to protect the developing offspring. How clever is that?!

They are quite identifiable as they have quite large, pale bands on their abdomen, except for the Early Colletes Bee (Colletes cunicularius). We have a new species of plasterer bee in the UK, called the Ivy Mining Bee (Colletes hederae), and it was first recorded here in 2001. It tends to be found in south Wales and southern England but it is spreading northwards. It can be seen foraging on flowering ivy, and it tends to nest in large aggregations. It’s definitely a species to look out for!

Flower bees (Anthophora spp.)

Flower bees will nest in a variety of places, such as in the ground, in cliffs and in hollow stems, depending on the species. They are large solitary bees, and can be mistaken for bumblebees.

An easily identifiable species is the hairy-footed flower bee, and they are called this because the males of this species have long hairs on their legs and feet! This species shows sexual dimorphism, which means that males look different to females, as the females are black in colour, with red/orange hair on their hind legs and the males are a dull brown/grey colour. They fly in a very rapid, darting sort of motion, which makes it very hard to take photographs of them.

Nomad bees (Nomada spp.)

Nomad bees are a cuckoo bee and are cleptoparasitic, so like the cuckoo, they lay their eggs in a host’s nest, and the larvae that develops will destroy the host offspring and eat their provision. These hosts tend to be mining bees. This means that they don’t build nests or provision their eggs with pollen and nectar, and therefore they don’t have any pollen carrying apparatus. These bees might seem like ‘the bad guys’ but they’re actually very interesting, and their presence is a good indicator that an area has a healthy solitary bee population.

Distinguishing different species of nomad bees can be pretty tricky, but they all look quite wasp-like, with yellow, black and sometimes red markings. They have pretty amazing eyes too!

So how can you attract these bees to your garden? Here are a few tips:

  • Reduce the mowing of your lawn. Solitary bees will forage on any wildflowers that come up, like dandelions and buttercups
  • Plant a variety of different pollinator-friendly flowers, with various corolla lengths. This will ensure that solitary bees with different tongue (proboscis) lengths will be able to access pollen and nectar. Back at home, my cornflowers seem to be popular with leafcutter bees and at my university, there is a patch of comfrey that is always buzzing with hairy-footed flower bees
  • Make or buy a bee hotel. A managed bee hotel is a great habitat for solitary bees, and they are great for both children and adults to observe. Abigail, one of the Garden’s PhD students, has written a fantastic blog about bee hotels which can be used to help you choose a bee hotel
  • Leave hollow stems for solitary bees to nest in
  • Leave bare patches of loose soil for mining bees

Also, if you see any solitary bees in your garden or when you’re out and about, you can upload your sightings to a site/app called iRecord. This means that you can contribute to crucial data about distribution of different solitary bee species and their conservation. Any records you can give will be very important!