The arrival of September at our latitude marks the time when windows closed all summer can be opened to admit cool night air. As I opened the window on our guest room, I was startled to see a wad of cotton-like material tumble from the upper window frame (above, placed on the concrete driveway for imaging).
My initial anxiety was that some sort of insulation was coming loose, but the original location of the material (photo below) ruled out that possibility.
My attention was now drawn to the contents of the mass, which to my initial dismay revealed an insect pupa and a number of living larvae:
After searching several combinations of key words in Google Images, I found one entry that matched my experience. The brief explanation there was that the mass was the creation of a solitary bee.
Now I did feel bad, because my wife and I are great fans of solitary bees. But armed with that clue, it didn't take long to track down the answer:
Anthidium manicatum, commonly called the European wool carder bee, is a species of bee in the family Megachilidae, the leaf-cutter bees or mason bees.I don't know whether the larvae in the photo are bee-related or parasites.
They get the name 'carder' from their behaviour of scraping hair from leaves such as lamb's ears (Stachys byzantina)... They scrape the hairs from the leaves and carry them back to their nests bundled beneath their bodies. There it is used as a lining for their nest cavities. Females tend to build their nests at high locations.