Some of the orders are rather unfamiliar, at least to people from temperate regions. Although only 30,000 species of Acari are known, there are so many undescribed species that Acari is almost certainly the most diverse group of arachnids. They occur in almost every habitat, including Antarctica, and many are important parasites of plants and animals. Other species are predators, fungal feeders, or scavengers. Although large blood-feeding ticks are the most familiar mites, most mites are less than 1 mm in body length.
Mites are the smallest chelicerates.
These animals resemble mites, but their legs are always longer than their body. These animals feed on smaller animals or are scavengers on fruit, vegetables, and especially on dead insects. It is a widespread myth that daddy-longlegs contain a powerful venom but are too small to bite humans in reality, Opiliones have no venom at all. They also differ from spiders in lacking the ability to make silk. There are about 5,000 described Opiliones species.