Located up on the balcony door to Willi and Gerda Beck's house in the village of Nußloch in Baden-Württemberg, the nest is approximately 2.5 metres across.
"Maybe it's not the biggest in the world – but the dimensions are definitely extraordinary and its shape amazing," said hornet-expert Melanie von Orlow of the nature protection agency NABU. She's especially amazed that the nature-loving couple is tolerating the hornets.
The nest only grew to its current proportions by chance. Beck's son-in-law suggested the family arrange to have the protected species moved. But when the 70-year-old Willi called a local nature warden, he was away on holiday. The second one was ill. When the third warden finally came to check out the situation weeks later, it was clear the nest could no longer be transported.
At the end of May, the hornet home was confined to the top of the opening for the window blind; now the Becks can no longer open their first story balcony door.
The good news? The insects don't appear to be dangerous. Von Orlow assured them that “hornets are more peaceful than wasps. As long as one doesn't shake the nest or manipulate it, everything is okay." A hornet's sting is also no more dangerous, she said. Besides, "whoever has hornets, doesn't have wasps."
"They leave us alone when we're in the garden," said 63-year-old Gerda.
In fact, the hornets eat many common garden pests, especially aphids. The buzzing colony also offers the Becks some in-house entertainment: they can observe the hornets' complex through the window.
The hornets, estimated to number between 700 and 1,000, don't bother Gerda, but she said her husband's a little squeamish.
The Becks have to put up with the hornets until the end of October, von Orlow said. By then, the insects will have left the nest and died.
"In September, though, there's still a lot going on – the nest might grow even bigger," she said.
Large hornet nests are normally found only in Bavaria and Baden-Württemberg in Germany, according to NABU.
The giant specimen in Nußloch is also a special treat for von Orlow, who said this year has been an especially bad one for Germany's hornet population.