You might even be an arachnophobe yourself. Many of the ticks and mites have a human host. Many more humans suffer from tick-borne diseases, such as tick fever and Lyme disease, than they do from scorpion and spider bites. Ticks and mites create high economic costs, due to the diseases they transmit to domestic livestock. For example ticks transmit biliary, Rocky Mountain fever, red-water, and tularemia.
Mites transmit Asiatic scrub typhus to humans.
Mites which are plant parasitic, and not animal parasitic, cause great damage to crops. For nearly every important commercial crop there is a parasitic mite that has to be guarded against. Scorpions and spiders are predators of other insects, and by consuming large numbers of insects are a great help in insect pest control. Not all scorpions, and very few spiders, are dangerous to man. Arachnids evolved about 500 million years ago.