Yesterday's Musing prompts a few thoughts on the scale of living organisms.
Humans are roughly a meter in size. Lice are a thousand times smaller. The bacteria that live on lice are a thousand times smaller still. Six orders of magnitude between humans and bacteria.
The largest creatures we know about are only one order of magnitude larger than humans -- great blue whales, for instance.
The smallest creatures -- viruses -- are only one order of magnitude smaller than bacteria, although whether you can count viruses as alive is a matter for debate.
I suppose you could also debate whether James Lovelock's Gaia counts as a living organism, in which case we jump six orders of magnitude up from the human. Teilhard de Chardin's Noosphere, which has come to pass as the global internet, has some properties of a living organism, with individual minds making up the "cells" of the "body." The Earth is as many orders of magnitude larger than a human as a bacterium is smaller.
Fred Hoyle's science fiction classic The Black Cloud imagines a living, intelligent creature that is another three orders of magnitude larger than the Earth.
Is it possible that out there among the galaxies there are evolving organisms on such a scale that we humans are as puny in comparison as a virus is in comparison with us -- an interstellar internet, so to speak? The speed of light would seem to be a limiting factor determining how large an organism could be and still function coherently. I suppose one could imagine a more languorous "life-style" than what we are used to, for which a million years is as a human second, but then one runs up against the age of the universe itself.
Still, look at yesterday's photo again, of a louse swinging from a human hair, and muster up a bit of respect for what we yet don't know about a universe (or universes) that may be larger and more complex than we presently imagine.