Backyard habitat: Mason bees

Mason bees

by Liz Magnanti

In North America there are about 4,000 species of bees. Four hundred of these reside in New York. According to the Bee Conservancy, one in four of these species is at risk of extinction and half of all bee populations are in decline. Bees are an important piece of our food supply chain, responsible for pollinating about one-third of our food supply. There are many things you can do to promote bees and other native pollinators in the garden and this article will tell you how to attract mason bees.

Mason bees are small, native, and for the most part nonstinging insects. They do not produce honey but they play an important role in pollinating food plants and flowers. Studies have shown that a single mason bee can pollinate as well as 100 honeybees! Mason bees are attracted to flowering plants and mason bee houses. They are known to pollinate many different types of plants including vegetables, fruit trees, crops, wildflowers, woodland and wetland species.

Mason bees are solitary, so they do not build a hive. They get their name from their behavior of using mud to build and seal their nesting sites which consist of small hollow cavities like plant stems, burrows, dead wood, rock crevices and mason bee houses. In the spring, usually early April when temperatures are above 50 degrees, male and female mason bees will begin to emerge. Males emerge first, and are only alive for a few days while they mate with females. Females will live for several weeks and spend their lives pollinating, laying eggs, and nesting. Shortly after mating, the female mason bee will begin her nesting process. She collects pollen and nectar from a variety of plants and places it in her nesting chamber. On top of this pollen and nectar she will lay an egg. Once an egg is laid she will seal the chamber up with mud and continue to perform the same process.

Inside this sealed chamber the egg hatches within a few days. The larvae will eat the pollen and nectar that the female has left behind. Once the food is all consumed the larvae will then pupate. The insect will stay in the chamber all summer, fall, and winter, until the next spring when it is time to emerge. Males are in the front of the chamber and females are towards the back—which is why the males emerge first.

One of the easiest ways to attract mason bees is with a house. A mason bee house consists of tunnels preferably 5/16” in diameter and six inches long. These are available commercially or you can make your own. I’ve seen DIY mason bee houses made of bundles of plant stems placed horizontally in tin cans attached to garden wall that attract bees. Having a house with the ability to remove the hollow tubes is ideal and the tubes should be changed every 2–3 years if possible.

Placement can make a big difference with attracting mason bees as well. Mason bees prefer a house that is stationery that does not hang or move around in the breeze. The front of the house should be facing south or southwest for the most exposure to sun. The house should ideally be in, or close to, a garden and several feet away from bird feeders, as birds may take some bees as a snack. Mounting the house at least a few feet off the ground will help protect it from predators and make them easier to observe.

One question I often get is how do mason bees find a house? My very non-scientific answer is, they just do! Having early spring blooms in the garden definitely helps, and you may have mason bees already and not even know it. It works the same way as a birdhouse. If the birds are around, you will most likely get something to use the house. You don’t have to worry about wasps using the houses either. They have different specs they look for when nesting and will not use a mason bee house.

Mason bees are a sign of spring and arrive in the yard and garden well before hummingbirds, orioles and other migrants. They are something I look forward to seeing every year and have been surprisingly easy to attract with just a little real estate.

Liz Magnanti is the new co-owner of the Bird House in Pittsford. ABOVE: Orchard mason bee, Osmia lignaria. Photo by Scott Bauer, USDA.