Here is a post that will help you, go to the two links in post 10, good info. https://www.backyardchickens.com/t/851351/mites-lice-first-time-pictures They can be around the birds vent, brown, white, red if blood filled, some are black dark like fleas, can be eggs a bases of feathers. The bugs will also leave fecal matter that can look like very small coffee grounds. When my birds had them I couldn't even see them. Birds were pulling feathers on back by tail and around the vent. Some had rough looking feathers and an unkept look. I used Sevin dust on them, found in the garden section of stores. 10 days later dusted again. Also cleaned all bedding out of coop, dusted the coop crevices, crannies, roosts, boxes. Gave them minimal bedding between dustings then after all clean gave them a nice layer of chips again. From what I have read here good to be on a maintenance program to prevent parasites getting a strong foothold. Diatomaceous Earth is not good for mites / lice or internal parasites, the parasites are not killed by the use or ingestion of DE by the bird.
Hi when my bird had mites she had no feather loss. I was ABLE too SEE the mites and eggs by looking at the base of the feathers near the skin. You will see whiteish egg sacks at the base. You will also notice what looks like soiled grayish dust on the base of the feathers near the skin. And lastly you will see tiny black bugs about the size of a pepper flake or smaller usually they are congerated where you see the grayish look to the feathers. You won't miss it if your bird has mites I'm speaking of the northern foul mite be cause they live on the body. But you do need to check your birds regularly. To do this look at the base of the feathers near the skin through out the bird including the crest. If they have the mites you will surely see tell tale signs.! Now their is another type of mite called the red mite.it does not live on the bird but lives in cracks and places in the hen house! It only comes out at night to feed on the bird. With that mite you might see feather loss and scabs. I hope this helps you out. If it's the northern foul mite very common then I doubt you can miss the signs. I hope this is helpful and wish you the best!
