We primarily see two types of mange in dogs: sarcoptic and demodectic mange. They are caused by mites - Sacroptes scabiei and Demodex canis. The former is a burrowing mite that can be transmitted between dogs.
These photos are of Demodex canis.

Demodex mites are a large genus of non-burrowing mites. Nearly every species of mammal has one or several species of Demodex that live commensally on the skin. They are ever-present but only cause a dermatological issue if the immune system is weakened.

In dogs that have hair loss that presents like mange we check for ringworm with a blacklight (it will fluoresce), check for fleas with a comb, and then lightly scrape the skin with a scalpel to collect a sample to examine under the microscope.

This sample was taken from a puppy that presented with hair loss. A skin scrape revealed a heavy load of Demodex canis - in healthy animals the Demodex population is much more sparsely distributed. We tend to see demodectic mange in puppies, senior dogs, and sick dogs.

If a pet has demodectic mange we also expect an underlying factor that may be contributing to immune suppression. In the case of the puppy - a heavy infestation of roundworms and hookworms. We treated with Nexgard or another acaricide and prescribed an appropriate dewormer.

If you love mites, give @amandy_lynn a follow.
If you want to learn more about Demodex in people, check out this DeepLook.

Fun facts: they eat sebum, don't poop, and their genetic lineage is intertwined with human migration
https://www.npr.org/sections/health-shots/2019/05/21/725087824/meet-the-mites-that-live-on-your-face