Fur mites are detected on their host. In severe cases, the mites are seen as small white dots in lively motion. In mild cases or if you suspect fur mite infection, you can collect materials from the fur in the following ways.
Brushing. Place the animal on some plain wrapping paper. Brush its back and sides for a few minutes.

Put a handkerchief or an equivalent over hose head of the vacuum cleaner and vacuum the animal’s back and sides for a few minutes.

Comb through the hairs of the back – especially the lower back – using a regular comb.

Place the material in a Petri dish and look at it under a microscope. In fresh material, living fur mites will often be found. Take a small amount of hair and spread it flat on the microscope slides with glycerin or the like. Place the cover glass on the material and examine it through the highly magnifying microscope. 100 x with phase contrast makes it easier to see the web. Look for the webs on the thinnest hairs. Most webs are found 2-3 mm from the hair root.

Other options
If you have seen the web, the matter is clear. No other species makes these kinds of webs in the fur of dogs, cats and rabbits. If one or more mites are found, Fig. 80 may be used for comparison, but remember that there many other species of mites in fur. These include house dust mites, storage mites, ear mites, Listrophorus mites and random mites from the nature. When examined for fur mites, you can also look for lice and fleas as well as their eggs and excrements while itch mites and follicle mites are not caught in this type of examination.