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Fall Care For Mason Bees

Excerpted from: Fall Care for Mason Bees

Mason bees are a group of bees in the Osmia genus. There are 140 species in North America. They are solitary, meaning that they don't live in a colony with other bees. Instead, the male and female mason bees live and work alone, except for mating. Mason bee females may nest together in mason bee homes we provide them.

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.

For more information on Mason Bees, see:
Mason Bee Profile

Bamboo Stakes Bee House When you put up a mason bee home, you 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.

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 (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.

Clean Cocoons

Mason Bee Cocoons 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.

Disinfect Cocoons

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.

Rinse Cocoons

Rinse the cocoons thoroughly. I do this in a sieve under cool running water.

Dry Cocoons

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 mold doesn't develop. Put the container in the fridge, or in an unheated garage or room. Monitor them for signs of mold. 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!

Mason bee hatching from cocoon In the spring, when temperatures are about 55° F, and fruit trees are about 25% in bloom, bring your cocoons outside and place them in an open container in the sunshine. The males emerge first, and do not sting. The females emerge a few days or weeks later.