A body length of 2 cm is well above average for modern terrestrial arthropods. Among mites, only a large and fully engorged tick would even approach this length. The largest known non-tick acarines are some red velvet mites that reach about 16 mm in body length. Most mites encountered in quarantine will be less than 1 mm in length.
The only acarines in the 5 mm–2 cm body length range are some ticks and red velvet mites.
Most of the major groups of terrestrial arthropods have most of their diversity concentrated in the under 5 mm body length range. Only some of the very large arachnid orders (whipscorpions, scorpions, sun scorpions) lack species in this size category.
Arthropods less than a millimeter in body length are properly considered microarthropods and include many of the animals that could be confused with mites. This is especially true of tiny spiders, opilionids, and a few insect groups such as scale insect crawlers that have a superficially mite-like appearance. Most of the arthropods that you encounter in this size category are likely to be hexapods, mites, or other non-acarine arachnids (e.g., pseudoscorpions, opilionids, or palpigrades).
The average mite has a body length of less than 0.5 mm, but several groups of soil microarthropods also have species in this extreme size range, including insects, springtails, proturans, copepods, palpigrades, pseudoscorpions and spiders.
Author: David E. Walter
Content last updated Sept. 2006, unless indicated otherwise
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