Carpenter Bees

In South Africa we have many species of bees, of which the honey bee is but one. Honey bees, as we know, are swarming bees, living in colonies. But there are many different solitary bees that live in isolation, but are nevertheless hugely important in the pollination of plants, including crop species.

The Carpenter Bee (Xylocopa genus) is one such solitary bee that pollinates – among others – tomatoes, beans, apples, granadilla, blueberries, potatoes and eggplants. They also pollinate indigenous plants such as the sea-rose (Orphium frutescens) – more of that later – and flowers of the pea family Fabaceae. Carpenter bees are often confused with bumble bees, but it’s easy to tell the difference.

It’s simple – we don’t have bumblebees in South Africa – or at least I hope we don’t. The Bumblebee (Bombus terrestris) comes from Europe and is already an invasive species in many parts of the world, where they were introduced to pollinate crops, especially greenhouse tomatoes, for which honeybees are not effective pollinators. This bee is now invasive in New Zealand, Tasmania, Japan, Chile, Argentina and Israel. This history of invasion means that if they were to be used for greenhouse pollination in South Africa, they would probably escape into the wild and become invasive here. Wisely, the SA government has not issued any permits for their import.

But we do have Carpenter bees. They are so called because they make their nests in dead wood – including the timber on your house. But don’t panic – their nests are quite shallow and are unlikely to cause structural problems. Don’t reach for the Doom – just provide alternative nesting sites. Leave plenty of old logs around the garden and don’t cut the dead inflorescences off your aloes. Carpenters just love the dried out stalks as nesting sites. They bore into the wood by vibrating their mandibles against the wood, but they don’t eat the wood like termites do.

Photos: Male Xylocopa caffra – Pinterest (left) | Female – Wikimedia Commons (right)

Carpenter bees are larger than honeybees, hairy, often colourful and their wings make a loud buzzing sound while flying. Male Xylocopa capensis are mainly black in colour but can range from greenish black to blueish black or purple. Females have white or yellow markings on the top of their bodies – one band on the thorax and one on the abdomen. Xylocopa caffra males, on the other hand, are all yellow in colour.

Carpenter bees have a fascinating pollination strategy – called buzz pollination. This can best be observed in the pollination of the sea-rose Orphium frutescens. If you go down to the coast in summer you may just see the carpenters at work.

Photo: Orphium frutescens – iNaturalist. Note the twisted anthers containing yellow pollen.

If you listen carefully, you’ll notice a change in the frequency of the buzz once the bee lands on the flower and clasps the anther. The note rises slightly to “middle C” as the rate at which it beats its wings changes.

The bee disengages its flight muscles from the wings to reduce unnecessary wing movement and uses these muscles to shake the anthers violently. The anthers respond to the sound frequency caused by the vibrations by opening up pores at their tips to shower the little insect in pollen. Through a pore you might ask? The beautifully twirled anthers of seemingly yellow pollen are just an illusion. The anthers are actually colourless and hollow and the precious yellow pollen is stored within, waiting to be released by this specialist pollinator. The carpenter bee eats some of the high-protein pollen and wipes the rest down its body to fill small sacks on the lower legs, ready to carry the plunder back to the nest to feed the larvae.

You may have noticed the antics of the yellow-haired carpenter bee hovering around a flowering shrub, then darting off, only to return seconds later to hover briefly again – what could be happening? This is the male Xylocopa caffra which is distributed throughout South Africa. When hovering around his patch of flowers, the normally completely yellow male lowers his abdomen and exposes two of his interstitial membranes which appear as two black bands on the abdomen. It is thought that he is releasing a sex pheromone as a female sexual attractant.

Photo: Male X. caffra fighting over territory – Warren Photographic. Note the visible black bands

The male is protecting a patch where females are likely to come to forage (not to mention responding to the sexy pheromones). He aggressively keeps other males out of his territory. If a foraging female is receptive she will allow the male to seize her in flight and carry her away ‘into the sunset’.

The moral of the story? If you want to attract insect wildlife to your garden, leave the garden a bit wild. No insect is attracted to concrete slabs or manicured lawns. Just relax, chill out, throw away the ‘pest’ control and watch the tiny visitors that will soon arrive to enthral you.