Safe Nests for Orchard Mason Bees (Osmia Spp.)
Most gardeners have heard of the benefits of our native mason bees as pollinators for fruit trees and that putting up nests can attract them to your garden. You may also have read (darn that internet!) that all you need to do is drill the right sized holes in a block of wood and put it out. BUT we now know doing that is being the bee equivalent of a slum landlord! If we are to provide nests, they must to be designed so cocoons can be removed and cleaned properly. Otherwise, after a couple of seasons, high numbers of pollen mites and other parasites build up in the colony. A colony can be so badly infested that many bees die in the cocoons and surviving bees have such high loads of mites they can’t fly and can only crawl around on the ground. Bees with lighter loads of mites leave mites behind on flowers to infect other bees.
In the wild, mason bees are naturally solitary. Each female finds her own hollow reeds, woodpecker holes or other sites to make mud cells for her eggs. When she is lured into sharing a multi-unit apartment house, however, there is a high risk of parasites building up in crowded conditions if the nests are not cleaned annually.
Friend the bees with well designed nests: There are several options for cleanable nests. You can buy split nest blocks of plastic or wood (e.g., see: http://beediverse.com/). These are designed to be disassembled to expose the channels with the cocoons. Another type of block has larger holes meant to hold disposable cardboard or paper tubes that are replaced every season.
Rather than using blocks, you can also just bundle 20-50 paper or cardboard tubes together (but not plastic straws). Wrap the bundle in something, such as bubble wrap or a thick layer of newspaper, to provide insulation. Slip the finished bundle into an open-faced container secured to a wall (see photo), which can be as simple as a recycled container or open faced wooden box or as elaborate as a decorative little bee house.
My own experience is that split blocks are expensive, but long-lasting and easy to use; it is, however, a pain to thoroughly clean out all those little channels. Paper tubes are time consuming to make, but cost nothing. They are easy to open and there is no cleaning chores. Likewise for the cardboard tubes, but they are fairly expensive. In a good year such as this one was, I have ended up pressing all three into service to provide nests for all.
Put up nests by March 1st where they will be protected from rain. The east wall of a building is ideal, where they can get the first rays of sun in the morning, but won’t bake in the hot afternoon sun. To protect them from attack by parasitic wasps and woodpeckers I move my nests into an unheated garage on July 1st for the rest of the season. Or you could leave the blocks out, but shield the nest holes using a piece of cardboard, wood or wire mesh.
To clean the cocoons: In late fall or early winter, get the cocoons out of split blocks or remove and open the tubes. Soak the cardboard tubes in a bucket of water for 30 minutes until the cardboard comes unglued. Unroll the paper tubes, which you can make yourself by rolling paper around a 5/16th inch dowel (instructions below).
Put the cocoons in a bowl of lukewarm water and swish them around gently until the mud and debris have been removed, then scoop them into a strainer. To kill the mites, either dip the strainer with the mites in a bowl of lukewarm water with 1/2 tablespoon of bleach or dish soap to 2 quarts of water. Then rinse well with clean water, and spread the cocoons on paper towel to dry. Large numbers of cocoons can also be cleaned by passing them through tubes of sand or shaking them in a jar of sand (see notes from Gord Hutchings: https://sites.google.com/site/hutchingsbeeservice/home)
Put the clean cocoons in a closed box or cottage cheese container with a loony-sized hole cut in one side. Store this emergence box in an unheated shed (refrigerators are too dry). Put the container outdoors by the end of February where it will be protected from rain and rodents near, or inside, your clean bee nest box. When bees emerge they will crawl out the exit hole and fly in search of new accommodations.
If you already put up nests that can’t be cleaned: If bees used them this year, all is not lost, but plan to start fresh next February. Find a cardboard box big enough to hold the nest block(s) with enough space for bees to get out of the holes. Put your nests in the box, close it up and cut an exit hole in the side of the box. When the bees emerge they will fly out the exit hole, but won’t be tempted to return to the old block because they can’t see the nest holes. Put the whole contraption outdoors by March 1st, under cover somewhere so the box won’t get wet. At the same time, put out your clean split blocks or bundles of tubes. When all of the bees have left that old block, get rid of it!
If cleaning cocoons sounds like too much work: There are other valuable ways to encourage native pollinators: plant a mixture of attractive bee flowers to bloom all season, leave undisturbed habitat for their nests (some nest in the ground) and, or course, never use pesticides.
Confused about their lifecycle? There is just one generation a year. Adult bees emerge from their cocoons in early spring. Each female searches for a suitable hole for a nest; when she finds one, she collects mud and fashions a cell at the back or bottom of the space. She stores enough pollen to supply one larva in the cell, then lays an egg and seals up the cell with more mud, leaving enough space inside for the larva to develop. She makes another cell in front of the first one, continuing until there are several cells in one hole. The deeper the space, the more cells she fits in. When the hole is completely filled with cells she caps the entrance with mud and moves on.
Each female lays 30-35 eggs and then she dies, usually in late May. Protected inside the cells, the fat white larvae eat the pollen supply and grow over the summer. In September, still inside the cell, each larva spins a cocoon and pupates inside (making the transition from larva to adult). Adult bees stay in their cocoons all winter and emerge in early spring. Cocoons are made of tough waterproof silk and can be handled and cleaned without injuring the bees inside.
How to Make Paper Nest Straws
Materials:
- An 8 mm (5/16 inch) wooden dowel, at least a foot long (longer is better)
- Large pages of light-weight paper, such as unprinted newsprint (e.g. from an artist’s tablet) or wrapping paper. If using printed newsprint, you will also need some sheets of white paper.
- Tape
Directions
Roll the paper around the dowel until it is 5 or 6 layers thick. If you roll at an angle, you will only need 1 small piece of tape to hold the tube from unrolling. This makes it easy to slit the tape when you want to unroll the paper later to remove cocoons. If using printed newspaper, roll one layer of white paper around the dowel, then roll the newpaper.
Slip the dowel out of the tube and trim the tubes to 15-25 cm long (6-10 inches). It is easier for bees to find their home straws if they are all different lengths.
Bundle 20-50 tubes together with the bottom ends lined up and wrap the whole bundle in insulating material, such as bubble wrap or many layers of newspaper. Slip the bundle into the container with the bottom end of the bundle tight against the back of the container so it is dark inside.
To learn more: I highly recommend this little book as it has everything you need to know: Pollination with Mason Bees by Margriet Dogterom. Available from: http://beediverse.com/; Foxglove Farm and Garden Nursery also usually has it in stock too.
Lots more about mason bees and other native bees Hutchings Bee Service: https://sites.google.com/site/hutchingsbeeservice/home)