Fall Care for Mason Bees

Mason bee female (Osmia lignaria)

We've gotten many requests from people for more info on mason bee care. While we don't currently have live stream capabilities for sharing our in-person workshops, we can write how-to's! If you are local to Squamish or the Lower Mainland, stay tuned for more workshop dates in the spring and fall. We hope this post is helpful for keeping your mason bees happy and healthy! 

What are mason bees? 

Mason bees are a group of bees in the Osmia genus. There are 140 species in North America, about 60 in BC! They are solitary, meaning that they don't live in a colony with other bees (unlike honey bees which live in colonies of 50-100,000 individuals). Instead, the male and female mason bees live and work alone, except for mating. (See lifecycle diagram below.) Mason bee females may nest together in mason bee homes we provide them, but they don't really interact with each other. 

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Mason bees are easy to miss- they look a lot like houseflies! They are usually dark and metallic blue/green around here, although they have longer bodies than houseflies and more distinct body segments (head, thorax, abdomen). Their bums are more rounded or "bullet-shaped" than other solitary bees that may look similar. A tip for telling flies apart from bees is flies have big bulgy eyes on the tops of their heads, while bee eyes are smaller and on the side of head (not counting honey bee drones). Flies have 2 wings, bees have 4. Another mason bee characteristic is they are only around in the spring- approximately from late February to June. The adults die after that. For that reason, they are great pollinators for early flowering crops, like fruit trees! 

The males are smaller than the females, have longer antennae, and often have fuzzy blonde moustaches- no joke!! The males can't sting, and while the females can sting, it's unlikely. 

Look at that moustache! Photo credit to http://blueorchardmasonbees.yolasite.com/

How do I "keep" mason bees? 

Mason bees do not require extensive maintenance like honey bees. You can simply buy or make a mason bee home (lots of style options, but make sure you can take the whole home apart to access cocoons in the fall, or use paper tube liners in drilled holes), mount it outside in late February/March, and wait for wild mason bees to find it. They will get busy laying eggs in the home, and then it's your job to clean the home in August-October, and store the cocoons over the winter to keep them safe. 

Why do I need to clean the cocoons and mason bee home? ​In nature their cocoons wouldn't get cleaned! 

​When we put up a mason bee home, we are encouraging the bees to lay a bunch of eggs very close together. In the wild, the bees would be forced to lay a few eggs over here in a hollow stem, and a few over somewhere else. With many nests together, it's easy for parasites to locate them and move from one nest tube to another. Your whole mason bee home could become a breeding ground for parasitic wasps, pollen mites, fungi, etc. over the winter (see photos below). So because we are setting up these unnatural situations, it's important for us to be responsible and give the bees a hand, so we don't do more harm than good. 

Parasitic mites in a cocoon we found this week. Dead adults below, live developing larvae in the cell.

How to Clean Mason Bee Cocoons

1. REMOVE COCOONS Open up your mason bee home or pull out and unravel the paper tube liners. (brown stuff that look like mini chocolate sprinkles is bee poop, aka frass, yellow/orange sticky stuff is pollen, light brown/reddish stuff that moves slowly are pollen mites.)

If you have a tray/routed house design, scoop out cocoons gently using a chopstick or tool designed for this purpose. Float the cocoons in a bowl of cool water. 

2. CLEAN Gently roll the cocoons with your fingers to clean off frass etc. You can also use an old toothbrush to gently scrub the cocoons. Cocoons can stay in water for up to an hour, but I usually only soak for a few minutes. Inspect cocoons for holes. If they have a tiny hole in them, parasitic wasps have gotten in, and the bee is dead. Cocoons that sink are dead. 

3. DISINFECT Scoop up cocoons and float in a bowl of 1L (4 cups) cool water and 1 tsp hydrogen peroxide or bleach. Swirl the cocoons around and let soak for a few minutes. This kills off any fungi and bacteria on the cocoons that could infect them later. Afterwards, disinfect the mason bee home by soaking in the solution for 15 minutes. 

4. RINSE Rinse the cocoons throughly. I do this in a sieve under cool running water. 

5. DRY Place your cocoons on a clean tea towel to dry. Roll them around a bit then let them air dry for a few hours. 

6. STORE Layer cocoons and crumpled up paper towel in a glass jar with many holes punched in the lid. The cocoons want to be dry and have air circulation so mould doesn't develop. Put the container in the fridge, or in an unheated garage or room. Monitor them for signs of mould. They want to be at about 60% humidity, and above freezing. Some say that fridges can be too dry for the cocoons. Try storing cocoons in a few different locations you have available and compare their hatching rates-then you'll know the best storage location for next year! 

7. HATCHING In the spring, when temperatures are about 12*C, and fruit trees are about 25% in bloom, bring your cocoons outside and place them in an open container in the sunshine. We tack a shallow yogurt container to the side of our house on the south side, beside our mason bee home. The males emerge first, and do not sting. The females emerge a few days or weeks later. 

Where to put your mason bee house

• In a sunny location. South or East facing is best to get morning sun. This helps the bees get moving early in the day. 
• Head height so you can see what’s going on, although the bees aren't picky about height. 
• Protected from wind and rain. 

This poor bee is emerging from a nest FULL of pollen mites. The bees can still survive, but it impacts their health over time. This mason bee home hadn't been cleaned in years.

1. Open up mason bee home. This is what you might find!

A pile of pollen mites. The move slowly

Step 1: Remove cocoons and float in cool water

Step 2. Gently remove frass by rolling cocoon between fingers or using a toothbrush

Step 3. Disinfect cocoons

Step 5. Air dry for a few hours

Step 6: Storage. Lots of holes poked in lid! Image from http://www.davidsuzuki.org/

Step 7: Hatching. Our high tech setup for emergence in the spring. We tack a shallow container to the side of our house just underneath our mason bee house. If it rains, it will stay dry, but it gets southeast sun to warm the cocoons in the morning. Avoid windy areas.