A common sight in many areas, gentle carpenter bees are the largest bees in Hawaii. Newcomers to the islands often confuse them with bumblebees as they are similar in size, but bumblebees are very fuzzy. In contrast, female carpenter bees are better described as glossy, solid black. Male carpenter bees are the blondes, sporting golden-orange coloring. Carpenter bees get their name from their inclination to tunnel into wood. The bees do not eat the wood, but use their strong mandibles to excavate tunnels. Inside the tunnels the females smooth out little cavities in which they will rear their brood.

Observe carpenter bees as they move through your garden and you’ll see how adept they are at gathering pollen, their protein source. Exploiting their larger size, these big gentle bees are masters of “buzz pollination” (also known as sonification). Landing on flowers, they use strong flight muscles like a vibrator to forcibly shake out pollen particles. Buzz pollination is important for many common fruits and vegetables, such as eggplants, peppers, tomatoes and blueberries.

Watch yet longer and you may witness carpenter bees cheating pollination altogether, using their mandibles to cut a slit near the base of deep throated flowers. Too large to enter the flower from the front, these bees make a shortcut to sip nectar, another food source. Honeybees and other beneficial insects often follow in their wake, visiting these perforated blossoms to gather a nectar snack.

Carpenter bees contribute greatly to pollinating local vegetables and fruits, especially the lilikoi. Lilikoi flowers are large and their reproductive parts rely on the visits of large insects or birds. Most insects are too small to successfully pollinate these big flowers, but carpenter bees have the right body size.

In nature, the preferred nest site of the carpenter bee is a dead tree branch or tree stump. The nest will begin with a female drilling a round hole about a half-inch in diameter. The female will then continue to excavate a series of tunnels and galleries, where she will lay eggs and bring a pollen mixture to feed the growing larvae. The young bees pupate in the cavities.

Carpenter bees must collect large amounts of pollen to feed their young, and their movements between flowers result in the production of larger and heavier fruits. Watermelon, squash, cucumber, zucchini, winter melon and kabocha pumpkin are all examples of local vegetables that benefit from carpenter bee pollination.

For more information about bees and bee-friendly farming, visit hawaiipollinator.com or uhbeeproject.com.

Build a nesting site

Farmers and backyard growers recognize the important services provided by carpenter bees. It is possible to encourage carpenter bees to nest closer to where you grow fruits and vegetables if you have the right materials.

Untreated wood: Pieces of untreated wood can be attractive to bees if they are at least 4 x 4 inches wide and about a foot long. To encourage drilling by the bees, make a couple of shallow holes. If the wood piece is standing up, drill on a side, against the grain. The bees will dig a tunnel and then turn to follow the grain of the wood.

Bamboo tubes: Bamboo shoots are a good alternative. Tie approximately 10 pieces of bamboo together. Each piece should be at least 3/4- to 1-inch diameter and about 1-foot long. One end should be open, allowing entrance to the future nest, and another should remain sealed by the natural partition of the bamboo shoots. Hang the bamboo nest bunch from a shaded tree branch with the open ends pointing down. If there are ants in the area, put a little Vaseline on the string or wire to prevent ants from attacking the nesting bees.

Ways to discourage nests

In urban areas, female carpenter bees will nest in fence posts, roof eves, railings and lanais. A single female causes little damage, but large colonies can be destructive.

Carpenter bees prefer unpainted, untreated wood. Apply paint or sealants to lanais and fences to make them less attractive to nesting females. Unpainted roof eaves facing the house, not visible from the front, are very attractive to carpenter bees. Be sure to paint these sections.

Seal existing holes from previous nests or large nails that have been removed as these encourage bees to drill their holes.

Source: Carpenter Bees, UH Honeybee Project, uhbeeproject.com

Jody Smith is a Certified UH Master Gardener on Oahu with UH CTAHR Cooperative Extension Service, she can be contacted at smithjos@hawaii.edu. Ethel Villalobos is head researcher for the UH Bee Project, she can be contacted at emv@hawaii.edu.