Mites belong to the group Arachnida which includes spiders, ticks, mites, scorpions and harvestmen (i.e. they are not insects).
Many thousands of mites feed on a corpse over the full term of its exposure to the elements. Gamasid mites like Macrocheles are common in the early stages of decomposition, while tyroglyphid mites feed on dry skin in the later stages of decomposition.
Some mites and carrion beetles have developed lifestyles that benefit each other. For example beetles from the genus Necrophorus find the ammonia excretions of blowfly maggots toxic, making it impossible for them to inhabit a carcass dominated by maggots. However these beetles carry on their bodies a type of mite from the genus Poecilochirus which feeds on fly eggs. If the beetle and its cargo of mites arrive at the corpse before any fly eggs hatch into maggots, the mites keep the maggot population in check by eating the eggs allowing the beetles to safely occupy the corpse.