Mason Bees

Today I finally got around to doing the long overdue cleaning of the mason bee house. I put a bee house in our yard a couple of years ago hoping to help increase the numbers of these threatened pollinators, and with the hope that their presence would increase my garden’s yield. Here’s a little more about mason bees from the Bee Diverse website:

In both cities and suburbs, we depend on wild bees such as bumble bee bees and honey bees to pollinate our fruit tree blossoms. Two species of parasitic mites have decimated our wild honey bee colonies (though beekeepers are able to keep mite levels down in managed honey bee colonies). The dramatic reduction in wild honey bee colonies has left us with very few honey bees in our garden.

One solution to this lack of fruit is to provide nests, as well as nectar and pollen producing flowers for local solitary bees such as the Mason bee. This will increase the number of Mason bees and provide the pollination level we need to get a reasonable fruit crop.

The Mason bee is one of many wild solitary bee species present in North America. It is friendly, and an efficient pollinator. They are called “Mason” because they construct walled-off chambers for each egg they lay. Mason bees begin working early in spring when flowers and fruit trees are beginning to blossom. After emerging from their cocoons and mating, the female Mason bees goes to work collecting pollen and nectar, while also pollinating your blossoms.

The mite problem makes it necessary to clean the house every fall in an attempt to control their numbers and reduce the chances that your bees will infect the next generation. A mite infestiation can apparently decimate a mason bee populations in 2 – 3 years.

Despite the name, adult bees don’t actually live in the bee house, they use it for laying their eggs, which grow to adulthood inside their cocoons, and hatch out when temperatures rise in the spring. The above photo shows the trays that sit inside the house. At first it doesn’t look like we’ve had much luck this year…

…but looking at the back of the trays reveals that there has indeed been some activity in the house this summer!

By removing the large black elastics that hold the trays together, we’re able to separate the trays to get a look at what’s inside.

Our house seems to be a desirable location for not only the mason bees (their larvae are the ones packed in mud at the top of the photo), but the leaf cutters also regularly lay their eggs in our house. I find it fascinating how each one is wrapped in perfectly shaped pieces of leaves.

Looking at the mason bees, I can see that it’s a good thing I’m doing a thorough house cleaning, as there were many tiny little mites crawling around the cocoons. The orange stuff in the cavities is pollen that the mother leaves for the developing young to eat. I don’t know for sure, but I suspect that the eggs in these cavities didn’t develop properly and that is why the pollen hasn’t been consumed.

We also found two stow-aways in our trays. They were fast asleep when I took the trays apart, but the warmth of the house woke them up, and they flew away before I was able to get them back into the clean trays.

Here are what the cocoons looked like fresh out of the trays. In order to stop the spread of these potentially devastating mites, it’s necessary to wash the cocoons in a very mild bleach solution. I was afraid of ruining their protective wrapping the first time I did it, but they’re very sturdy and stand up to their baths extremely well.

While the cocoons were laid out to dry, I scrubbed the trays and house to remove any traces of mites.

Here are the freshly cleaned cocoons. Each one contains a fully formed adult mason bee that will hatch once the weather warms up in the spring. I have to be careful to return them to the cold garage or put them in the fridge fairly quickly, as they will start emerging if kept at room temperature for too long.

In late winter/early spring, I will set the cocoons out in the “attic” of the bee house, where they will pupate and begin their work of mating, laying eggs, and providing pollen and nectar for their developing offspring, continuing the cycle.

For more information on Mason Bees, and to see a photo of one, click here.