12 June 2019

The mystery of the "cotton" in the window frame - updated x4

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.

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.
I don't know whether the larvae in the photo are bee-related or parasites.

Reposted from 2016 because this week I was wandering through the "gardening" section of our local Target store and found this:

The shelf tag erroneously said "butterfly house."  The label on the product was slightly less inaccurate with "insect house."  It is in fact a structure designed for solitary bees.  There are online instructions for making these as a DIY project, but this one was nicely made and inexpensive.  I'll hang it from a shepherd's crook near ground level in our garden and hope to see some of the tubes getting filled as the summer progresses.

Here is a photo of an equivalent bee-condo viewed in cross-section:

This one was made by drilling holes in a wood block (presumably with a removable flap so the curious home scientist could inspect the process and the season progressed).

If I remember, I'll try to post followup photos in the summer and autumn.

Updated May 2018 to show the bee "condo" installed in our back garden -

Helpful hint:  A "shepherd's hook" (used for hanging flower baskets, bird feeders etc), when purchased from a home decor or gardening store can be somewhat pricey.  I went instead to our local farm supply store and picked up the "pigtail" post shown in the photo (used on farms for stringing electric fences around fields) for about $2.  An added advantage is the little S-shaped part at the bottom which grips the post for stepping it into the ground and digs into the ground to provide 2-point stability for the post.

Updated again:

Well, back to the drawing board.   After a week of drenching rains, the "bee condo" was in multiple pieces.  I don't think I can blame raccoons, because there was no honey or larvae in it yet.  Wind might have banged it around a bit, judging from the current position, but I rather suspect this was assembled using water-soluble glue.

It was cheap.  You  get what you pay for.

Fortunately I have several rolls of duct tape in the garage.

June 2019: Reposted for the fourth time to add new information.

I was able to duct tape that contraption back together and it has survived a year of biblical rains and 25-below-zero temps.  Not sure how much it's being utilized; I should do a survey of it later this summer.

But this week I saw a post at Neatorama with new information about backyard bee houses, citing a Gizmodo article entitled "Your Cheap-Ass Bee House is probably Killing the Bees" -
The most prevalent problem with bee houses is that when they’re not cared for properly, they can become breeding grounds for pests, mold, fungus, and disease...

Pollen mites are one of the biggest threats to the habitability of bee houses located in humid environments or built of materials like bamboo that don’t dry easily. “If there’s no way for moisture to dissipate from the nest then the mites take over,” Purrington said...

Packing a bunch of [normally solitary] species together into one box is not only ecologically weird, it can make them targets, Mader said. “The cheek-to-cheek occupancy of bee houses helps predators (woodpeckers for example), parasites (including wasps, mites, and others), and diseases find a dense host-bee population to exploit.”..

... it’s bad for bees when a house is tied loosely to a tree or a post with a string rather than tightly secured in place... “The bees can’t land if it’s flapping around in the wind,” he said of mason bees. “They’re terrible at landing.”

...it’s a good idea to cover the houses with metal netting to keep the birds out, as woodpeckers and bluejays find bee houses to be great restaurants.
You learn something every day.


  1. Wow. That's pretty amazing bee behavior.

  2. hi
    They look like bee larvae;

    Various ways to make your own nestbox;

    and you can buy viewable tubes;
    I've also seen folks use perspex tubes wrapped in dark paper.
    cheers another phil (not sure if my links are working)

  3. We have beehives and was sitting on the deck by the lavender and noticed a bee-like non honeybee in the flowers. Was absolutely amazed by my discovery and eventually managed to find out it was a wool carder bee, first discovered in NZ in 2006. The males are supposedly aggressive but there was nothing but harmony in the flowers :)

  4. This is a cool post. Thx for sharing.

  5. In the last couple of years I have started noticing and appreciating the world of native bees. Have done some reading and observing and bought a small mason bee house for my balcony garden. It's a fascinating exploration and I am just getting my feet wet, but here a few links:

    https://crownbees.com/ - a source for native bee supplies and lots of information

    https://www.goodreads.com/book/show/28783027-mason-bee-revolution - an introduction to keeping mason bees, written by Crown Bees' owner, Dave Hunter

    https://www.goodreads.com/book/show/34303588-our-native-bees - interesting look into the world of native bees

  6. In the last couple of years there has been growing interest in Australia in what we call "bug hotels". Various gardening programs have had segments on making your own. A google search with those terms may offer a wider variety of styles and methods for anyone thinking of making their own.

  7. A search of 'mysterious cotton wool in aluminium window frames' lead me here! I live in the North Island of NZ, in the Bay of Plenty. Last year I found what looked like cotton wool packed into a several of my window frames, and after finding this blog and a few other sites I sat outdoors for a while waiting to see this amazing little carder bee. It didn't take long before it made an appearance, along with many others at various points around the house. As much as I like bees, I don't like them in the window frames and they sometimes come into the house and frighten my little boy. I've since had to place a small piece of mesh over the holes to keep the bees out and installed a few bee houses outdoors. The bee house seems to be working well, the carder bees are still busily working away and myself and my son can watch them from a safe distance.

    1. I'm glad you found us. Hope you can stick around and browse some of the categories in the right sidebar. :-)


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