Where have all the carpenter bees suddenly gone?

Dear friends and supporters of the foundation.

We already reported on carpenter bees (Xylocopa spec.), a very special species of wild bee, in a blog post on 17 July 2022. These are wonderful, large, blue-black bees. In recent weeks, we have received many enquiries from interested bee lovers asking why they are suddenly no longer to be seen in gardens.

This has also been the case at our research base since around mid-September. We were able to observe a large number of carpenter bees this year, which was certainly due to the fact that our clary sage was in magnificent bloom for months. This undemanding plant is one of the preferred destinations of these bees, which also love to visit sunflowers. And suddenly, we don't see any anymore.

This is because the male mason bees die in early autumn and the females move into their winter quarters. The bees often use the breeding sites that were created for their offspring in spring and summer. These are often found in dead wood, stacked firewood and rotten tree trunks.

Firewood piles are popular with carpenter bees for building nesting sites.

There, the carpenter bees use their strong jaws to gnaw long tunnels, often with branches and brood chambers, into which they lay their eggs. These brood chambers also offer protection from rain and frost in winter and are then used as a nest for hibernation.

Tunnels and brood chambers of wood bees in dead wood

A female carpenter bee usually lives for up to a year. In our region, with its mild winters, females can also live for several (2-3) breeding seasons.

Male carpenter bees only live for a few weeks, or in exceptional cases a few months. Their only task is to find a mate and fertilise the eggs. After that, they die.

The female carpenter bees that were fertilised in autumn are inactive from this point on, in a state known as diapause, which is comparable to hibernation. This ends when temperatures rise in the coming spring.

This naturally raises the question of how the queen fertilises the eggs laid in spring without any ‘males’. This is made possible by a sperm storage organ in the bees' bodies called the spermatheca. The fertilised eggs develop into female carpenter bees, while the unfertilised eggs hatch into males.

This closes the circle and the new bee year can begin for the carpenter bee. One final note: female carpenter bees can sting, but they only do so when they feel extremely threatened. Even then, their stings are harmless and nothing like those of honey bees or wasps. So despite their imposing appearance and size, there is no need to be afraid of these companions.

We are already looking forward to the awakening carpenter bees next spring.

Warm regards and be(e) good,

Yours sincerely,

Klaus Heinzel