Most mammals have mites that live in their fur and that don’t usually seem to do them much harm. People don’t have these mites, probably because we don’t have much fur, but other primates do. These ectosymbionts are highly specific to their particular hosts and are modified in various ways to cling to their hosts hairs. They slide up and down the hair to access their food (which mostly seems to be oils and other fatty materials) and probably to regulate their temperature.
In the case of the koala fur mite, Koalachirus perkinsi (Domrow), the first two pairs of legs and their bases tightly clasp a hair of the host (you can see a ventral view of the mite with the groove that receives the hair here). This particular mite came from a sickly koala at a rehabilitation centre. Too ill to spend much time grooming (which usually keeps the population in check), the koala was literally crawling with mites and I was brought a large vial of them to identify.
Much to my surprise, when I opened the vial a horde of mites scrambled out and dashed helter-skelter across my desk. Although the front legs look inappropriate for mad dashing, they have slender pretarsi that are folded out of the way when riding the hair. When unfolded they are capable of surprising bursts of speed, which I suppose helps them get from one koala to another.