There can't be a bathroom in Britain where steam doesn't sometimes condense on cold windows at this time of year - and wherever moisture accumulates around window frames bathroom mould is sure to grow, unless you dry the windows very thoroughly every morning.
So while I was laying in the bath yesterday I wondered what the mould looked like that I could see was beginning to grow in the corner of the uPVC window frame, and today I scraped a tiny amount off - about enough to cover the head of a pin - and had a look at it under the microscope at x 40 and x100 magnification.
The fungal hyphae were pretty uninteresting but the animal life that was living amongst them was fascinating, and included three of these ....
..... delightful little tardigrades.
Tardigrades are minute but complex animals that are also known as water bears or, in the US, moss pigs. Most of them live in mosses, stabbing moss cells with mouthparts that resemble aphid stylets and then sucking out the cell contents.
These three, that were about a fifth of a millimetre long, must have been feeding on the bathroom window mould. If there were three in the tiny sample that I collected, there must be vast numbers on houses where the fungus is allowed to grow unchecked around condensation-soaked window frames.
These are lively little animals with a brain, complex digestive organs and two eyes....
.... that you can see in this higher magnification view. The arrow-shaped structure between the eyes is the stylet, used for feeding, with a muscular pharynx at its base.
Tardigrades have eight stubby little legs, each equipped with a pair of claws that are visible on the end of one leg in this image. This makes them particularly adept at clambering through the branches of a forest of mosses - or through the fungal hyphae of bathroom mould.
You can find a wonderful scanning electron microscope image of a tardigrade by clicking here and a long article in American Scientist on these fascinating animals by clicking here.
So how did they arrive in the bathroom? Almost certainly via their minute eggs which are carried everywhere on the wind.
These animals are totally harmless but I guess you might find the thought of numerous tardigrades crawling around wet window frames as either fascinating or disgusting; if it's the latter and you are about to rush off and douse your windows in disinfectant, just ponder this.
When dry conditions prevail, tardigrades survive by producing drought resistant eggs that are amongst the most indestructible living organisms on the planet. When they are in the egg stage (known as the tun stage) they can survive immersion in boiling water and liquid nitrogen and can survive for decades before they hatch again. Your disinfectant won't have much effect on the eggs, even though it'll kill the adults.
But, most remarkably, these are the only multicellular animals that have ever travelled in outer space without a space suit and survived, when they were flown as tuns in the Space Shuttle - a feat that no human will ever equal. They deserve some respect. For a detailed account of their adventures in outer space, click here and here.
Something I'll ponder when I'm laying in the bath tonight and watching the condensation trickling down the windowpane.
You can find some more pictures of tardigrades, this time extracted from mosses on our garage roof, by clicking here.