Will boric acid work better than borax to kill bird mites?

If the mites eat the boric acid, yes. Boric acid is a stomach poison. The borax available on the market is a detergent containing boric acid salts. It works by surface contact, dissolving the cuticle of the exoskeleton and dehydrating the insect.

A much faster way to kill bird mites is the use of a pyrethroid insecticide, which interferes with insect nervous systems. Diatomaceous earth is slower but still faster than borates.

Catsmine - is it true that bird mites are extremely difficult to get rid of, no matter what method?

Catsmine - is it true that bird mites are extremely difficult to get rid of, no matter what method?

The problem is always getting rid of the source. Often that is a bird's nest in the eaves or a rodent's nest in the walls. Once the source is removed, eliminating them is fairly straightforward.