Pollinator Houses

How to build a bee block

Of all the bees native to North America, about 30% use some kind of tunnel in which to lay their eggs. The diameter of the tunnels, as well as their preferred length, varies with the different species of bee. So, to attract a wide variety of native bees, it is best to use a wide variety of tunnel sizes.

The most popular bee tunnels range from about 3/32” to 3/8” wide. The narrower ones are usually shorter (about 3-5 inches ) and the wider ones are longer (up to 6 inches). These numbers are not exact, so approximations work fine. The tunnels are easily made with a long drill bit in blocks of dimensional lumber or in the ends of bucked logs. Three important points:

  • Use untreated wood
  • The tunnels should be as smooth as possible
  • The holes should not go completely through the wood (one end remains closed)

    Nest box with ready-to-hatch straws nearby.

Although most native bees are solitary in the sense that one female raises a family by herself, the members of a species like to live near to one another. For that reason, you should group tunnel sizes together. In other words, one block may have lots of ¼-inch holes, while the next block has lots of 3/8-inch holes. Space the holes at least ½- to ¾-inch apart—the larger the holes the bigger the spacing.

If at all possible, line the holes with paper straws or rolled wax paper. A paper liner does two important things:

  • It keeps the inside of the nest smooth and snag-free
  • It can be replaced every year, thereby reducing the accumulation of diseases and parasites.

The paper tubes can be gently withdrawn at the end of the season and stored in a cool dry place. Alternatively, the cocoons themselves can be taken from the paper and stored separately. In the spring, the paper tubes can be hung near the nests or the cocoons can be put in an open-ended container—like a pvc pipe or a small flower pot—from which the bees will emerge.

Hang your bee boxes at least three to four feet off the ground so they don’t disappear among the weeds and to keep them away from splashing water and small animals. Early morning sun is okay, but the boxes should be protected from direct afternoon rays. Additionally:

  • Add a small overhanging roof to keep out the rain
  • Mount the boxes on a steady structure rather than one that sways in the wind
  • A loose covering of wire mesh (like chicken wire) can help deter hungry birds in winter

That’s really all there is to it. For maximum protection against disease build-up, boxes can be sanitized with bleach at the end of the season or replaced altogether after two or three seasons. In any case, always use liners for best results.