Mite identification by trained taxonomists depends on microscopic features that may require clarifying, dissecting, and mounting specimens under a high-powered compound microscope. Rapid sorting of mites is achieved by ecologists by using “morphospecies”: taxa that look different from each other at relatively low magnification. We know that there is error associated with this approach. It is far better to “split” species (identifying the same species as more than one thing) than to “lump” species (to call more than one species the same thing); the first can be corrected in the data, the second would require re-sorting.

Mites have eight legs. If a mite appears to have six legs, it is either a larval stage, or it may not be a mite (ex. collembola or insects).

Mites have variable numbers of different developmental stages. A general scheme is: prelarva, larva, protonymph, deuteronymph, tritonymph, adult. In some taxa however, one or more stages from this sequence may be absent.

Do female and male mites look different? In oribatids, the only noticeable difference is that males are about 20% smaller than females. In mesostigmata (“predators”), the venter may have a completely different arrangement of shields.

Do juvenile and adult mites look different? Some species look dramatically different. Oribatid juveniles are generally pale, while adults have a dark, hard exoskeleton with distinct ventral marks and plates. Some species, like the “leafy mites”, have complex body ornamentation that is absent in adult stages. The differences are so vast, only oribatid taxonomists can associate juveniles with the adult stages. With other groups, such as the mesostigmata, the juvenile and adult stages look similar. There may only be differences in the extent of shield development, and slight colour variation.

Is there size variation within a species? Within the same stage of a mite life history, there is not much variation in size of individuals. If we have two adult oribatids, one being twice the size of the other, they are not the same species. Juveniles may appear to vary in size, but this is most likely caused by comparing specimens in visually similar, but different developmental stages. Collembola, however, can show a great range of size variation within a species.

Spiders are difficult. The individuals that show up in our samples tend to be juveniles. It is often challenging to match up juveniles to adult stages. Characteristics that tend to be consistent include the pattern and features of the eyes, shape of the cephalothorax (particularly in lateral view), relative positions of the spinnerets, and number of tarsal claws. Adult males and females also look different. Adult males have swollen, sclerotized distal segments of the pedipalps (the "boxing glove"). Penultimate males (one molt away from adult) can also have swollen, but not sclerotized pedipalps (more "oven mitt" than "boxing glove"). Adult females are distinguished by the sclerotized epigynum on the ventral abdomen. Males may also have narrower abdomens than females.

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