A shiny giant – The violet carpenter bee

Have you ever had a big black insect flying into your field of vision and making you step back in surprise? That was probably Xylocopa violacea, a mostly harmless solitary bee.

published on: 8/2/2023

written by: Priska Flury

Carpenter bees can sometimes be confused with bumblebees. However, bumblebees usually have translucent wings, whereas the wings of carpenter bees are blue or black shimmering. They also usually have a hairless and shiny abdomen. Image: Wikimedia Commons/Daniel VILLAFRUELA, CC License

Profile

With a size of up to 2.5 cm, Xylocopa violacea, the violet carpenter bee, is the biggest bee species in Switzerland.
It is commonly known by many names, such as the violet carpenter bee, the common carpenter bee and the blue carpenter bee.
The genus Xylocopa belongs to the order of hymenopterous insects and contains over 730 species worldwide¹
In Switzerland, only 3 species of Xylocopa are native: X. violacea (violet carpenter bee), X. iris and X. valga.
Xylocopa violacea can be found all over Switzerland on elevations up to 1 500 m. It is the most widely distributed carpenter bee in Switzerland.
It prefers sunny sites such as orchards, gardens, parks, and forest edges.

Classification

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Apidae
Genus: Xylocopa
Species: X. violacea

Life cycle

Violet carpenter bees, as most Xylocopa species, are solitary bees, meaning they don’t live in a hive and do not have a queen. Usually, they nest in deadwood excavating tunnels with their powerful mandibles, which is what gave them the name carpenter bee. They use the chewed wood to form nest cells within the tunnels. In each cell, eggs are laid and supplied with pollen-dough, a mixture of pollen and nectar, for the larvae to develop properly. The cells are then closed using small pieces of chewed wood. The tunnels are excavated by single individuals and can be 40 cm in length. In some species of carpenter bees, freshly emerged females wait in their natal nest, hoping to inherit it, when their mother dies. Excavating a new tunnel is very exhausting and found to consume nearly as much energy as 7 hours of flight. Reusing or sharing a nest seems to offer an advantage even if it means that your own reproduction is delayed.

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Violet carpenter bees are univoltine, meaning they produce only one generation of offspring per year. When the adults emerge in late summer, they search for proper hibernation sites, which often are old and abandoned nest tunnels. The hibernated adults can be observed again in early spring, when they fly out looking for suitable mating partners and later for nesting sites.

Not a bright outlook

Contrary to popular belief, carpenter bees do not eat wood, but rather pollen and nectar. They play an important role in the ecosystems since they are excellent pollinators. Many of our crop species such as tomatoes, eggplants but also ornamental flowers are pollinated by them. Carpenter bees are polylectic, meaning they feed on many plant species from different plant families, such as Fabaceae – e. g. Alfalfa (Medicago sativa), Lamiaceae – e.g. common sage (Salvia officinalis), or Asteraceae – nodding thistle (Carduus nutans). Unfortunately, all three species of carpenter bees in Switzerland are at risk. For a long time, deadwood in forests or parks had been regarded as useless and cleared away, eliminating suitable nesting sites. You would contribute to the survival of this beautiful and useful species, if you left dead wood lying in your garden instead of removing it.

Did you know?

Male carpenter bees were observed to mimic stinging attacks against potential aggressors even though they are stingless. However, female carpenter bees can sting but they are not particularly aggressive and sting only as a last resort.² Their venom though, has been reported to be painful and in one instance to kill a small bird.²

References

Gerling D et al. 1989. Bionomics of the large carpenter bee of the genus Xylocopa. Ann Rev Entomol,34:163-190. http://dx.doi.org/10.1146/annurev.en.34.010189.001115

von Reumont BM et al. 2022. Venom profile of the European carpenter bee Xylocopa violacea: Evolutionary and applied considerations on its toxin components. Toxicon: X, 14:100117. https://doi.org/10.1016/j.toxcx.2022.100117.