The carpenter bee – friend or foe?

We usually think of carpenter bees as those bulky, black bees that buzz loudly around our yards and burrow into wood, earning them a reputation as pest insects to be eliminated. You might be surprised to learn better side of these interesting native bees!

Three different species of large carpenter bees live in California, all belonging to the genus Xylocopa. The one usually seen in our area is the Valley carpenter bee (Xylocopa varipuncta). The females of this species are common and instantly recognizable: black and slightly hairy, with black eyes and shimmering dark wings.  The males are seldom seen but stunning: slightly fuzzy and rich golden-brown in color, with a yellowish head and mesmerizing olive green eyes. Their appearance has earned them the moniker “teddy bear bees.”

Valley carpenter bees (Xylocopa varipuncta). On the left is a black female dusted with yellow pollen (perched on a passionflower, with a honeybee in the background). On the right is a golden-brown male (perched on the flower spike of a Mexican bush sage). Photos © Kathy Ikeda

Despite their somewhat startling size and sound, these carpenter bees aren’t as scary as they might appear. Male carpenter bees can’t sting, and females will sting only if disturbed (and even then, that threshold is high). Their large body size and relatively small wings make their flight look aerodynamically impossible and even comical at times!

Large carpenter bees have earned their name — and a bad reputation — by their practice of nesting in wood. They don’t construct hives like honeybees; instead, the females use their strong mandibles (jaws) to chew a small round entry hole and a narrow, six- to ten-inch-long tunnel into soft wood or the trunks of dead trees (cottonwoods and plane trees are favorites). They then use the leftover sawdust from tunnel excavation to wall off a series of brood cells inside the tunnel. A large mass of pollen and nectar is deposited in each cell, then a single large egg is laid on each mass. The eggs soon hatch and develop into adult bees, which remain in the nest until spring.

Preventive measures are the best way to prevent any structural damage from carpenter bees. They won’t disturb painted, varnished, or treated wood and they will avoid holes and cracks that have been sealed or caulked, so regular home maintenance is an effective deterrent. They also won’t tunnel into composite wood decking. Steel wool stuffed into the nest entry holes will discourage carpenter bees from returning, but the nests must be empty for this technique to work. For more specific information, visit the University of California Integrated Pest Management (UC IPM) website: https://bit.ly/2KSq9jM

Pest control companies used to recommend insecticidal sprays and dusts to eliminate carpenter bees from homes, decks, and other wooden structures. Fortunately, that practice is changing as researchers learn more about carpenter bees’ habits and their beneficial role in our natural ecosystem. As one expert notes, “their contribution to pollination far outweighs any damage to structures.” Also, our California carpenter bee species are far less destructive than other species in the eastern U.S.

Chemical control should never be used as a first line of defense against carpenter bees, because the recommended insecticides also can be lethal to honeybees and a wide range of other beneficial insects (See https://bit.ly/2zj5rVI).

You can encourage large carpenter bees to nest in a non-damaging way by placing a scrap piece of untreated 4×4 redwood post or a log section in a sheltered place in your garden, and pre-drilling it with some shallow holes. The bees will find and enlarge the holes.

California is also home to thirteen bee species in the genus Ceratina, collectively known as small carpenter bees. They look nothing like their better-known relatives; they are tiny (less than ¼ inch long), have narrower abdomens, and are metallic greenish-black in color. They bore into and build their nests inside pithy or soft-cored stems of plants such as elderberries, agave, cole crops (Brassica), and sunflowers. This nesting behavior does not harm the plants.

Both the large and small species of carpenter bees act as valuable pollinators. They visit a wide variety of native plants, ornamentals, and some crops, feeding on the sweet liquid nectar from the flowers and collecting pollen to feed to their young. When they do this, they facilitate plant reproduction by carrying pollen from flower to flower. Read more about carpenter bees and their roles as pollinators at https://bit.ly/1DprK8k.

Narrow, tubular flowers present a special challenge for the large species of carpenter bees; the bees are too big to squeeze inside them to get to the nectar and pollen. In these cases, the carpenter bees engage in nectar robbing: they land on the outside of the flowers and use their sharp mouthparts to pierce them and drink the nectar inside. This doesn’t harm the blooms, but it also means that the bees don’t come in contact with the pollen-laden structures inside the flowers, and in these instances, no pollination occurs. Fortunately, large carpenter bees also visit and are able to pollinate wide variety of plants with more accessible flowers, and the smaller species of carpenter bees — unlike their larger cousins — are able to climb into tube-shaped flowers and pollinate them.

I’ve spent many hours in my garden in close proximity to these fascinating insects, observing them without worry. Valley carpenter bees constructed a nest in our redwood arbor many years ago, but we leave them undisturbed, because their limited burrowing doesn’t compromise the structural integrity. It’s been fascinating to watch them fly in and out of the small nest hole and visit nearby perennials, including two of their favorites, autumn sage and foothill penstemon. I’ve been able to photograph the bees up close and to watch them as they hover nearby; I’ve never once been stung, and have been well entertained.

My carpenter bee verdict: Definitely a friend!

To learn more about the highly diverse species of bees in our state, read the book “California Bees & Blooms: A Guide for Gardeners and Naturalists,” published by Heyday Books. For gardening-related questions, call the UC Master Gardener office at 209-953-6112, or visit our website.

 

 

 

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