Habitat Feature: Bee Houses

Photo © henryleelucas

There are more than 4000 native species of bee in North America, many of which can be found working alongside the well-known honey bee (Apis mellifera) pollinating plants. The honey bee, while very important to agriculture, is a nonnative species; it was brought to North America from Europe and is now considered “naturalized” (established and widespread in the wild, though not indigenous)open_in_new. Bees are incredibly busy, not just collecting resources for themselves but also pollinating trees, shrubs and wildflowers, as well as most agricultural products –it is estimated they are responsible for pollinating one third of our food supply. With the recent decline in many pollinator species, and an increase in public concern, it is important to understand the ecology of these beneficial insects so we can better provide appropriate habitat for them.

The history of agriculture and the sole use of the honey bee for pollinating services has lead to risky farming. These days many growers are relying on the exceptional pollinating power of local solitary bees. The video above describes how these bees are so efficient.

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Photo © One Tam, S. Rae, deedavee easyflow, Bob Peterson

Prior to the introduction of honeybees, native solitary bees were the most ubiquitous bee pollinating in North America; today these species pollinate side-by-side in most ecosystems. Unlike the social, hive-nesting honeybees, solitary bees nest as individuals. Most are ground nestersopen_in_new like bumble bees and sweat bees, but many, namely mason bees and leafcutter bees, are cavity nesters. Cavity nesters lay their eggs in small holes–like those in wood made by birds and insects, or in dried hollow reeds or stems. They start by filling the back of the cavity with nectar and pollen then depositing an egg and sealing it with mud or chewed leaves in a mason-like fashion.

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Photo © tpjunier

In the image above of a European red mason bee (Osmia rufa) nest, you can see the pollen, the translucent egg, and the mud used to line and seal each chamber. The female will fill a nest tube with individual chambers then seal the end and will not share a nest tube with another female. Larvae develop inside the nest, nourished by the pollen-nectar ball. After spinning a cocoon and pupating, new adults become dormant and remain in the cocoon until the next spring. Since the resources these bees need are natural and easy to provide, we can help support solitary bees by providing flowering habitat in our landscapes. These efficient pollinators are likely to return the favor and improve pollination in our personal gardens.

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Photo © Rob Cruickshank

Solitary bees are gentle, easy to attract, and are very efficient pollinators known for their energetic nectar harvesting techniques. As a solitary bee, they do not live socially in a communal hive. The cellophane bee, above, is a solitary bee that makes its nest in bare ground. Another common type of solitary bee to attract to a garden are the mason bees. There are about 140 species of mason bees across North Americaopen_in_new. The males do not have a stinger, and the females will only sting if trapped or squeezed. This makes them an ideal neighbor for the home garden, since they pose little threat of stinging. Mason bees are cavity nesters and you can invite them, and their pollination services, to your garden by providing a bee house.

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Photo © Timo Newton-Syms

A bee house is a simple and attractive addition to any yard or garden space that will provide habitat for solitary cavity-nesting bees. A bee house is simply an artificial nesting structure that mason bees, and other solitary bees, can use to lay their eggs. Ideally, a bee house provides a safe space away from predators, weather, and chemicals–all of which can interfere with a successful reproductive cycle. You can find bee house for sale online and sometimes in gardening stores and nurseries. Although many styles of commercially made bee houses are available, a large number of the designs may unintentionally put bee larvae at risk. Plastic or glass tubes can hold moisture, promoting fungus and bacteria. The necessary hole diameter is sometimes specific to local species, having an inappropriate sized tube hole can promote parasites and predation, and the designs often offer no way to clean or replace used cavities.

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Photo © Tom Brandt

An excellent option is to build one yourself. There are several common designs but it is important to make sure you can open the bee house or remove the tubes after they are filled. Some plans create a bee house by drilling holes into stacked blocks of wood, shown here. Others bind cardboard or paper tubes, or dried-out hollow plant stems together in decorative containers. Both options mimic the habitats bees would naturally use to nest in and will allow you to monitor the house and replace parts as necessary to make sure you are providing a safe place for nesting bees.

To build your own bee house:

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Photo © John Hritz
  • Start with a frame. A wooden box that’s open on the front side is a good place to start. Include a roof or cover to deflect rain. The frame should be about eight inches deep to fit long tubes.
  • The bee house should be closed on the back end (i.e. only one entrance). The holes should be two to ten mm in width to accommodate multiple species of native bees. If you get them too big, you may attract predators like wasps and ultimately endanger the bees that you’ve invited into your yardopen_in_new.
  • Tubes can be paper or cardboard, bamboo, or hollow reeds. If you remove invasive reeds like Japanese Knotweed or Phragmites, these make good hollow stems when cut and dried. A win-win!
  • Make sure your bee house is firmly fixed to a wall, a tree, or the ground; it should not shift around or sway in the wind.
  • Place the bee house in the sun, facing south or southeast to catch the earliest morning heat, as mason bees require morning sun to warm up and get going.
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    Photo © Ron Cogswell

    Although cavity nesting bees will nest in holes drilled into blocks of solid wood –this mimics beetle holes in branches and logs, it is not the recommended method for making bee houses. Solid blocks of drilled wood do not allow for opening or cleaning and allow pests and pathogens to build up and contaminate your bee house. In nature, cavities are rarely used twice by a mason bees helping to minimize the exposure of larvae. If you do use drilled blocks they should be replaced each year; or, you can use replaceable cardboard inserts and paper tubes like the native bee house pictured. Inside the drilled holes, you can see the white paper tubes that can be removed and replaced after the nesting season.

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    Photo © Penn State

    Inviting mason bees and leafcutter bees to use the bee house you’ve provided will require the appropriate habitat surrounding the nest. Bees need pollen and nectar, and lots of it. Solitary nesting bees need up to four times the amount of pollen and nectar for reproduction than hive nesting beesopen_in_new. They do not want to travel far to get it either, usually staying within 100m of the nesting area. That means they need a diverse native flowerbed nearby with plants producing blossoms from March to June for spring mason bees and from June to August for summer-season leafcutters. Include native fruit-producing trees like cherries and crabapples, specific to your region, which have some of the earliest blossoms of the season and asters and goldenrod to extend the blooms into fall. Native plants are important to pollinators because they have the morphology that allows bees efficient access to nectar and pollen; and, native plants can contain chemical compounds bees seek out to self-medicate to combat mites and pathogens.

    Pro Tip

    Bee-friendly native perennials can be found in your ecoregion guide that you can find by entering your zip code under the Explore Tab.

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    Photo © poppet with a camera

    It won’t take long for locals to discover this convenient nesting place and take-up residence. Natural nesting locations, like logs, and snags are often a limiting resource in many areas where such dead and dying wood is considered undesirable and is removed. Providing bee houses in your gardens helps to return an essential part their resource needs. The bee house above is, you can see, quite successful. The mason bees are just finishing up the final seals at the end.

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    Photo © henryleelucas

    To be successful, cavity nesting bees need quality mud and leaves to separate each chamber and to seal off the end to protect from predators and parasites. Mason bees need moist clay soil, free of gravel, grains of sand, or bark, within 50-100 feet from the nest. Providing mud may be as easy as digging a small hole somewhere in the garden, about a 10 inches deep to get past the topsoil and get down to the mineral clay. If your soil is sandy, rocky, or too dry, you can provide the right mud from another source by filling the hole with it. A lack of clay-like mud is a large reason bee houses are unsuccessfulopen_in_new.

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    Photo © Orangeaurochs

    Harvesting cocoons may be the key to bee abundance and health. Like birdbaths, nest boxes, and other habitat features, attracting wildlife to your yard comes with the responsibility of making sure they are not being lured into a trap. It should take no more than a couple hours to harvest and clean the cocoons from a colony of 25-40 tubes. This process will help ensure the hard work your mason bees have put into rearing young will be both successful and will increase the number of active pollinators in your garden the following year. Harvesting the cocoons from a bee house protects them from being eaten by birds or parasitized by wasps. It will help you control the environmental conditions during their dormant period and the timed release of new bees in the spring.

    Harvesting bee cocoons from your bee house.

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    Photo © Chris Worden

    Spring mason bees will fill the tubes by the end of spring. To protect against predation and parasites, once you see the holes plugged and no more activity around the house, remove the tubes and put them in a safe place (like under an inverted bucket or a cardboard box with a few holes in the top). Then, replace the tubes. Summer leafcutter bees, shown here, are just emerging from their cocoons from the year before and will continue the pollinating and cavity nesting. Collect and protect their full tubes in the fall and store them in a cool dry place for the winter.

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    Photo © Orangeaurochs

    In the fall you can open your spring mason bee tubes or open the stacked blocks and remove the cocoons. You may find little black drops of larvae waste or other tiny, sometimes colorful, spots which are various types of mites. To remove, place in tepid water, gently rub, rinse in sieve until water runs clean, and place on paper towel to air dry. Examine, and repeat if necessary. Place the dry cocoons in a breathable container and store in a cold dry spot. A refrigerator is a good place. The larvae are dormant and the cold temperatures allow them to use fewer resources.

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    Photo © Ian Boyd

    In the spring, when there are flowers to pollinate, remove your bees from the refrigerator and place near your clean and empty bee house, with nearby native flowers and mud resources. Place a third of your cocoons out every two weeks to prolong their pollinating season and to avoid losses from a late frost or other environmental pressures. Your new bees will help support your garden and use the bee house you’ve provided to continue the cycle, increasing your pollinator power annually.

    Interested in spreading the word about native Pollinators?

    Visit our Bee Care Outreach Materials section and download a powerpoint that you can present to your local gardening or conservation group, nieghborhood, or friends and family. Quick Guides are also available to keep track of key information and seasonal timing of raising native Bees.

    How to add a solitary bee house to your map

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    Photo ©

    First, place the bee nest object on your map. It is located in the Tool Shed under Third. Scroll to the right using the arrows on the toolbar that pops up to find bee nest. Click the bee nest once to select it. Then click on the map where you would like to place it and drag it open to the size you’d like. You can always change it’s size and position using the lock/unlock from editing box.

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    Photo ©

    Double click on the bee nest to add important data and show off your conservation efforts. You can give your bee house a name in Basic Information. Then click Characteristics to tell us about it.

    Bee Nest Season Letting us know when you have nesting bees helps to identify the types of pollinators you are promoting.

    Bee Nest Hole There are a number of materials and set-ups that can mimic the natural environment native solitary bees use for nesting. Let us know how you prepare your bee house.

    Cocoons Harvested Harvesting cocoons in the fall helps protect the pupae inside from predation, parasitism, and, often, the harsh effects of the elements.

    Don’t forget! You can also make comments about the bee house and upload pictures of it. We want to see you busy bees at work.

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