Mason Bees

Traditionally, Mason bees (Osmia) are thought to have been given this name because they make their nests out of wet mud. But this has been invalidated by the fact that it is simply the common English name for their Latin genus “Osmia”. 

Mason Bees — What Are They?

Mason bees belong to the genus “Osmia” and the family “Megachilidae”. There are about 500 different Mason bee species but only around 20 reside in the UK — the most common being the Red mason bee (Osmia bicornis). 

They are a variety of solitary bee which means they don’t live in colonies like the famous bumblebee. Instead, they prefer to live their life alone.

Their Life Cycle

Akin to the Leafcutter bee, Mason bees emerge around Spring time after their hibernation and development period. 

You will notice the males out and about first so they can wait for their future mates. At this stage, there is a lot of competition for the males who buzz avidly around the nest and trying to put off their man-friends.

When the females finally decide to emerge, the males quite literally pounce on them! Then, the mating process begins.

Quickly after the deed has been done, the males die while the female hunts for the perfect spot to lay her eggs. Once she’s found the right place, she’ll start collecting pollen and nectar to put in each cell (one larvae per cell). Typically, the female Mason bee will construct between 4 and 10 cells each. 

It takes a lot of work for the females to provide enough pollen and nectar for just one of their eggs. They have to visit approximately 1875 flowers just to offer up enough pollen for a single larva. Talk about hard work!

Mason Bee larvae
The larvae of Mason Bees within cells of a mud nest.

Nesting Habits

They are a cavity-nesting type of bee which means they love crevices in walls, hollow plant stems and even vacated snail shells. 

As soon as the female has laid an egg in a section, she will use mud to block it and form partitions between the cells.

What Do Mason Bees Look Like?

It’s quite easy to distinguish a Mason bee (Osmia) from other types of bees since they fly extremely fast and don’t have pollen baskets. They carry pollen in their abdomen hairs instead.

Regardless of the type of Mason bee, they sport dashing metallic colours like black, green, and even blue in some cases!

They’re quite interesting to observe. Many enthusiasts have spent hours upon hours filming and studying these magnificent creatures, capturing their erratic flight paths and nesting methods.

Can Mason Bees Sting?

These bees aren’t aggressive at all — the males don’t even have a stinger!

With that being said, if you manage to squeeze a female Mason bee in your hand, she will sting (but who wouldn’t, right?).

Overall, they are extremely gentle and won’t hurt you unless you hurt them. 

Are They Endangered?

Mason bees themselves aren’t endangered. However, a few years ago, a statistic was released stating that 40% of pollinator insects are in danger of becoming extinct. If this doesn’t make you want to go and start building a bee house right away, we don’t know what will!

Are They Good Pollinators?

Mason bees are extremely good pollinators! It has been said that a couple of female Osmia can pollinate an entire apple tree

But, more than that, they are incredibly hard-working, regardless of the weather. Even when it is a cooler day or it’s raining, they will still work, whereas other types of bees (like the honey bee) will stop. 

To attract Mason bees to your garden, you will need to keep a few things in mind:

  • Location
  • Housing
  • Pests and predators
  • Mud
  • Plants

Let us take a look at each of these in turn so you can provide the best 5-star destination for these fantastic pollinators.


As long as you put your bee house in a great location, they should come to you pretty quickly. Why? Because they know they will be protected from a variety of harmful sources like predators and adverse weather conditions.

Water should not be able to fall into the nest and it should be placed in a prime position for sunlight (ideally somewhere they will receive the sun in the morning). Also, think about where the warmest place during winter is and try to position your bee hotel there.


There are two types of housing you can try out — DIY or pre-made houses. 

If you purchase a pre-built one, it will last longer than any you build yourself. However, the cheaper option is to create it by hand — and it’s somewhat simple to do, although you will need a few DIY tools to hand.

Once you’ve built (or bought) it, make sure to hang it between 4 and 7 feet from the ground.

Pests and Predators

Predators and pests will find it difficult to gain access if you elevate it (and we strongly suggest you do!). 

However, winged predators that eat bees (some species of bird) will still be able to get to them. You can combat this by attaching mesh around your bee hotel

Throughout the year, you’ll have to inspect your nest to ensure no diseases or pests are already present. If you find them, you can wash the cocoons out and clean it every so often.


Mud is what Mason bees (Osmia) use to build their nests and cells.

Select an area of your garden to turn into a wet mud plot (ideally near their housing location) so they can get to work and create their nests much faster. 

All you have to do is dig a hole, line it with some polythene paper, shift the soil back into the hole and add water. It’s really simple to maintain too — just put the hose on it a few times a month (depending on how much rain you’ve had).


Wildflowers are the best for all types of Mason bees. The females need the pollen and nectar for their hatched larvae to eat before they make themselves a cocoon and transform into adults.

Think about planting poppies (Papaver somniferum), alyssum (Lobularia maritima), black-eyed Susans (Rudbeckia hirta) and asters (Symphyotrichum). Each of these bloom at different times during the year which will keep bees happy all year round. 

So, there you have it, everything you will ever want or need to know about the beautiful Mason bees (Osmia). Remember to always think about the importance of our bees and do all you can to protect the UK from experiencing bee shortages. 

The Incredible Mason Bee
The Incredible Mason Bee book by Steven Scanlan and Catherine Scanlan, is an informative resource that will teach you more general facts about this species and everything you need to know to help the dwindling population of Mason Bees pollinate our world.

Get The Buzz!

Sign up to receive our newsletter!

Get helpful information about bees and gardening advice on the different ways you can help the UK's bee population!

You can unsubscribe at any time.