Mites on a midge. Coloured scanning electron micrograph (SEM) of mites (order Acarina) on a midge. A mite is a small arthropod, related to spiders. Mites are found on a wide variety of insects, plants and animals. On insects, such as this midge, they feed on the bodily fluids. If there are enough mites infesting the insect, they may kill it. Magnification: x50 when printed at 10 centimetres wide.