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Native bees are a vital part of our environment. They ensure healthy wildflower communities and harvests of fruit and vegetables. Native bees are suffering from extensive use of pesticides and the fragmentation and loss of habitat.

Although flowers that provide nectar and pollen are important, a lack of nesting sites is probably a greater threat to native bees than a lack of flowers. Unlike butterflies and other pollinator insects, bees make nests in which they create brood cells for their offspring. In many modern landscapes, a desire for neatness has resulted in the removal of bare ground, dead trees, and untidy corners of rough grass-all important nesting sites for bees.

The good news is that there are several easy ways to make bee nesting sites. Providing suitable nest sites is one thing we all can do to improve our gardens, parks, and wild areas for these important insects.

Nesting sites for solitary wood-nesting bees
The great majority of bees nest on their own, many in holes in wood. For wood nests, providing a range of hole sizes between 3/32" and 3/8" (2.5 mm to 10 mm) in diameter will support a wide variety of bee species. These types of nests need to be placed so that the open holes face the morning sun. Not only will this warm the nests earlier in the day so the bees will become active, but it will also prevent them from overheating in the hottest part of the summer afternoons.

(1) Nesting blocks. Bee blocks can be made by drilling nesting holes between 3/32" and 3/8" in diameter, at approximate ¾" centers, into the side of a block of preservative-free lumber. The holes need to be smooth inside, as deep as possible, and closed at one end. The length of the lumber is not critical-8" or more is good-but the lumber should be at least 4" deep. This block can be fixed firmly to a stake, fence, or building, or placed in a tree.

(2) Twig bundles. Some plants, like teasel and bamboo, have naturally hollow stems. Cut the stems into 6" to 8" lengths. Be careful to cut the stems close to a stem node to create a tube with one end open and the other closed. Take fifteen to twenty stem pieces of a variety of internal diameters and tie them into bundles with the closed ends of the stems together. Fix each bundle to a stake, fence, or tree with the stems horizontal to the ground.

(3) Logs and snags. Place logs or old stumps in sunny areas. Those with beetle tunnels are ideal. "Plant" some upright (mimicking dead trees), to ensure some of this deadwood habitat stays dry. On the southeast side of each log, drill a range of holes. Make the interior of the holes as smooth as possible, because bees may avoid rough holes.

Nesting sites for solitary ground-nesting bees
(1) Bare ground. Simply clear the vegetation from a small patch of level or sloping ground and gently compact the soil surface. This potential nesting area should be well drained and in an open, sunny place. Inevitably, different ground conditions-from vertical banks to flat ground-will draw different bee species, so create nesting patches in different areas if possible.

(2) Sandpits and piles. In a sunny place, dig a pit about 2 feet deep and fill it with fine-grained, pale-colored sand. The pit must be able to drain; otherwise, the nests could flood. Where soils do not drain well, a sand pile of a similar size and materials as the sandpit can create suitable nesting conditions. If space is limited, fill planter boxes with sand; the advantage of planter boxes is that they can be placed at any angle, even on end to form a vertical bank.

(3) Bumble bee nests
Unlike the nests built for solitary bees-who can be very particular about hole diameters-there are no strict size requirements for bumble bee nests. After emerging from hibernation, a bumble bee queen will hunt for a dry, warm cavity in which to start her colony. Any hole large enough for a small colony will be fine. In natural conditions, most bumble bees nest in abandoned mouse holes in the ground or under grass tussocks.

A simple wooden box, with internal dimensions of about 7" by 7" by 7", made from preservative-free lumber will work. Drill a few ventilation holes near the top (covered with door screen to deter ants) and some drainage holes in the bottom. Make an entrance tunnel from 3/4" plastic pipe, marked on the outside with a contrasting color, and fill the box with soft bedding material, such as upholsterer's cotton or short lengths of unraveled, soft string. The box must be weather tight; if the nest gets damp, the larvae may become too cold, and mold and fungus will grow.

Where to put your bee nests
Location of the nesting sites is important. Wood-nesting bees prefer sites that are sheltered from the worst of the weather, with entrance holes facing towards east or southeast to get the morning sun. Most bees cannot heat themselves efficiently and need the sunshine, especially in the morning, to provide enough warmth so they can become active. Place the nests between two to six feet above the ground, and fix them firmly so they don't shake in the wind. Ground nesting bee species will avoid wet soil, so choose areas of dry, well-drained ground, preferably south or southeast facing.

For bumble bee boxes, choose an undisturbed site, in partial or full shade, where there is no risk of flooding. The box should be on or just under the ground. If you bury it, extend the entrance tube so it gently slopes up to the surface. Put your nesting box out when you first notice bumble bees in the spring, or when the first willows and other flowers are blooming, and be patient. There is no guarantee that bees will use your box. Only about one in four boxes get occupied. If it has no inhabitants by late July, put the nesting box into storage until next spring.

Since bees need nectar and pollen to supply the brood cells of their offspring, all nesting sites should be among or close to suitable foraging plants. If both nesting sites and foraging areas are near, bees will be more likely to occupy the nests.

Produced by Matthew Shepherd, Pollinator Conservation Program, Xerces Society
April 2004

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