Pseudo-Microcaddisflies
This common name refers to only one genus.
These are often called Pseudo-Microcaddisflies.
These very tiny caddisflies (hook size 24-28) are not very important to anglers, because of both their size and the fact that they prefer warmer water. On rare occasions they are abundant enough to be significant.
None of the books I've checked suggest which individual species are important.