They are quite small -- less than an eighth of an inch long, as I can see on those rare occasions when they briefly land, apparently to feed on something too small for me to see. When they fly, it is impossible to determine their size. In fact, it is impossible for the eye to follow an individual for any length of time. When the light catches them, they are like swirling motes, and might be mistaken for dandelion fluff. Then they turn and seem to simply wink out of existence. As each one loses the light, the eye is drawn to the others still visible among the hundreds which are flying about. They dance and sparkle, hover and flit, appear and vanish, all on some insect business of their own, describing complex fractals in the afternoon air, unaware of how they dazzle and delight with their aerobatics.
If I listen very closely, I can imagine that I hear the collective beating of their tiny wings as the faintest of buzzing, there on the edge of perception. It is probably an illusion. Sooner am I likely to hear the rustle of the short green grass in the breeze, than the beating of wings so small, however many there might be. Perhaps the cats are able to hear them. I can merely watch, and wonder at the strangeness of their brief lives.