Boring Buzzers: Carpenter Bees

Every few months when we step out onto our little sit-out deck in the morning, we find pockets of sawdust strewn on the floor. Initially we thought that it was termites that had started eating away at the old wooden pergolas over the deck. But a general check could not reveal any other tell-tale signs of termites. So we continued to be baffled about what was responsible for this.

One morning as we sat there we saw a large black bumble bee flying about the pergolas, and then quite mysteriously disappearing somewhere into the wooden beam. A closer examination revealed a hole in the wood, and it seemed to be the one into which the bee had vanished. So now we had a possible suspect, but as yet no confirmation of the link between the sawdust and the bee. The next time there was sawdust, we checked the wood just above it and sure enough we found a neat hole. The next step was to find out if a bumble bee could also be a boring bee!

Some preliminary research confirmed one suspicion—that the drilling in the wood was indeed the work of a bee. But it also refuted the supposition that this was a bumble bee. What we discovered was that this was a bee called the Carpenter Bee, and also many interesting facts. 

To start with, of course, the name. Carpenter bees are aptly named for their habits of drilling into wooden surfaces such as logs and tree branches, or in urban areas, wood used for construction. They drill a neat hole in the wood and tunnel into the wood in order to make their nest and lay their eggs. In a couple of hours the carpenter bee can drill a hole a few inches deep, leaving beneath the debris of sawdust.

Source: en.wikipedia.org

Carpenter Bees (Xylocopa latipes) are one of the largest bees we have here in India. They are big and black with an intimidating appearance. Their wings shine in the sunlight with metallic blue, green and purple colours. The male and the female are more or less similar, but the male has hairier legs.   

Carpenter bees do indeed resemble bumblebees, but while bumblebees usually have a hairy abdomen with black and yellow stripes, carpenter bees typically have a shiny, hairless abdomen. The two bees also have different nesting habits–bumblebees nest in an existing cavity often underground (e.g., in abandoned rodent burrows), whereas carpenter bees tunnel into wood to lay their eggs.

Another distinguishing feature of Carpenter bees is that they are solitary bees, unlike most other honeybees and bumblebees that live in colonies and are known as social insects. The honeybees make hives, while carpenter bees excavate and make well structured tunnels in wood. They vibrate their bodies as they rasp their mandibles against the wood.

After boring a short distance, the bee makes a right angle turn and continues to make a tunnel extending about 30-45 centimetres, parallel to the wood surface. Inside the tunnel, five or six cells are constructed. Each cell houses a single egg, and each one is provided with a wad of pollen collected from flowers, which could serve as nourishment for the larva when the egg hatches. Each cell is then sealed with regurgitated wood pulp and saliva. The larvae feed on the high protein and calorie pollen beebread, and enter hibernation, before they turn into adult bees and emerge from the tunnel. Adult females can live up to three years and can produce two generations of offspring per year, though they never see their offspring!

What an amazing feat of insect architecture was going on, hidden from us, in the single beam of wood right over our head, as we sipped our morning tea!

Equally impressive is the contribution of these bees to the cycle of nature. Carpenter bees typically visit large open-faced flowers which have a lot of pollen as well as nectar. They use vibrations to release the pollen from the flower’s anthers, and are described as buzz pollinators. As they feed on nectar from many flowers, the pollen from the flowers sticks to the underside of the abdomen and the legs, which is transported from flower to flower as they flit and settle to feed, playing a vital role in pollination.

Curiously while I have seen the bee hovering around the wooden beams, I have yet to see one buzzing around the flowers. So the next step in my tracking the bee’s journey still remains incomplete. Even the drilling seems to happen after dusk, as the saw dust appears only in the morning, when the bee appears to be rather ominously hovering around, guarding the entrance to its nesting tunnel, and then flying off into the sunlight.

Interestingly, despite their intimidating appearance, it seems that the males are harmless and do not sting. Female carpenter bees can inflict a painful sting but will seldom do so — unless they are handled or bothered by people– another difference between these solitary bees and other bees and wasps that inflict dangerous stings.

While carpenter bees are have their own place in nature, when they start their drilling activities in wood in houses and gardens, they can become pests. As they hollow out the wood, this can lead to the deterioration or collapse of wooden structures. With our already old and weather-worn wooden beams starting to become favoured nesting sites for Carpenter bees, we had to look for ways to stop these boring buzzers. Research indicated that one option was to inject chemical insecticides or pesticides into the holes. We could not bring ourselves to do this.

We then read that these quiet-loving bees do not like vibration or noise around their nests, but seeing as they were happily drilling right next to our large and loud wind chime, this was obviously not bothering them.

Another thing that these bees are said to be very sensitive to is citrus scents near their nest, and spraying citrus oil into the holes was a recommended way to foist them off. We have arrived at our version of this by plugging the new holes with wedges of lemon. We think that this is playing some part in preventing their access, so one battle at a time is won. But this has certainly not deterred their efforts at drilling new holes; so if the hollowed-out beam collapses on our heads one fine morning, the bees would have won the war! 

–Mamata

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