What is this under the wings?

[Rowanh16]

I don’t like getting hands on so this is my dad looking and seeing this stuff. It looks crumbly but when he pinches it it doesn’t crumble. When my mom saw she said maybe yeast since it’s been a hot muggy summer. Does anyone recognize this? It’s only under the wings and only our middle aged laying birds who are 3 years old not our 6 month ones nor our 10 year hen

 

[ChicNmom]

Is it stuck to the feathers or can it be rubbed off?

 

[Sally PB]

It looks like it could be lice.

 

[EggSighted4Life]

I don’t like getting hands on so this is my dad looking and seeing this stuff. It looks crumbly but when he pinches it it doesn’t crumble.

It's lice nits.. see following link for examples and identification..

https://the-chicken-chick.com/poultry-lice-and-mites-identification/