This is the tiniest thing I've tried to photograph. I'd guesstimate about 3mm, but I really need to pick one of the cilantro flowers that it favors and measure one of the petals (it can fit comfortably on a single petal.)

This creature moved slowly and sat still for extended periods -- the only reason I was able to get any shot at all! I could barely see it on the flower, though admittedly I do have some eyesight issues.