I’ve worked on some fairly small things, spending many hours looking down a microscope. I’ve described a species of louse that was just over 1 millimetre in length, and also some nematodes that were slightly less than 1mm long. But these are all relatively gigantic when compared with the wasp and protozoans pictured above (the scale bar is the same for each of the three, and btw, there are 1000 micrometres in a millimetre).
I was alerted to a blog post (here), discussing some research on how fairy wasps (Megaphragma mymaripenne), smaller than most unicelluar eukaryotes, can actually function. I’ll let you go there yourselves. I won’t discuss the nitty-gritty as it would either be gilding the lily, because the other blog post already exists, or some form of plagiarism! But, their ability to function on such a tiny scale has a lot to do with the fact that the wasps have been able to jettison the nuclei in their cells, amongst other things.
What I found most amazing though, was that the fairy wasp, at 200 microns is only the third-smallest insect ever recorded. The smallest and second-smallest insects are also both wasps.