What happens when Mason Bees fly?

What happens when Mason Bees fly?

Your bee house is set up, the weather is warming, your fruit blooms are open, and your mason bee mud supply is ready – what happens when mason bees start flying?

This stage of raising mason bees is what I like to call Wait & Watch and it’s the best part of raising spring mason bees.

Male mason bees emerge first and find a good waiting spot.

You can identify male mason bees by their smaller size, their long antennae, and their white tufts of facial hair. They are handsome and refined gentlemen. Female mason bees can take two weeks longer to emerge and you can identify them by their larger size and their large mandibles (jaws), used to carry mud and build protective mud walls. Remember to be patient to see bee activity at your bee house because it is the female bees, not the male bees, who visit and sleep in the nesting holes.

Once out of their cocoons, the bees clean themselves, warm up, and release their first waste - a tan substance that is called meconium. When you see these small tan dots on your bee house it's a good indicator that the mason bees hatched and took flight. People often mistake the meconium for fungus but there is nothing to worry about and only the freshly emerged adult bees produce meconium.

After mating, the female mason bee will choose her nesting hole and mark it with her scent and solitary bees do not share nesting holes.

Starting at the back, the mother bee builds a series of nesting chambers made up of a pollen loaf, a single egg, and a mud wall. It takes about 25-30 trips worth of gathering pollen and nectar to build each pollen loaf. To build a mud wall requires about 6-8 trips of mud gathering. At the open end of the nesting hole, the mason bee adds an extra thick layer of mud to protect the last chamber. The extra thick layer is called a capped end and it lets us easily see that a mason bee finished her nest.

Watch as capped ends are filled with mud.

When you see about 4 out of 10 holes filled you should add more nesting holes if needed. Each female bee is able to fill more than one nesting hole and they need extra space to move in.

One of my favorite things to do while mason bees are flying is to stand a few feet away from the front of the bee house and watch female bees come and go.

You can stand still if you need to but mason bees are not as shy as other hole-nesting bees. A bee will go in head-first, do her chore, and turn around inside to emerge head-first again. Pretty often a bee will go into the wrong nesting hole and arguments between the two bees commence. To show how gentle mason bees are I like to tell the story of how a mason bee hit me in the nose on her way out and just flew away. In the mornings it's fun to watch the bees peek out and start to sunbathe before flying.

The theme of the first few weeks of mason bee activity: be patient. Remember that it takes time for a female mason bee to emerge, mate, get to know her new home, and start building a nest. Female bees are hard to see as they work in the very back of the nesting hole.

Pro Tip:

• At night you can shine a flashlight into the nesting holes and look for shiny mason bee bums or heads.

A word about the weather:

Mason bees love spring weather. Their dark color soaks up the warmth of the sun and they will fly in poor weather. They will not fly in heavy rain, hard winds, or weather that is too cool (like a cloudy day with highs below 50F). Mason bees will simply wait out bad conditions either under a leaf or, for female bees only, inside their nesting hole. If you are releasing mason bee cocoons in waves, be sure to check for a good stretch of a few days of mild weather.


• For staggered release: check the weather forecast for stretches of good weather
• Ensure that your mason bee mud source stays moist
• Add fresh nesting holes when you see 4 out of 10 filled with mud
• Still waiting for spring? Keep your cocoons in the fridge at 34F/1C