The tiny red "spiders" commonly found in gardens and on farms are not actually spiders but are a type of arachnid called spider mites. Spider mites are considered pests, live in large groups, and feed on a large variety of plants.
Spider mites are common in North America. They are very small, with the largest of the species being only 1/20th of an inch long. They are spider-like in appearance with eight legs and an oval body. Also known as webspinning mites, they get this name from the silk webbing they create on the underside of leaves. The mites reproduce quickly and under the right conditions can complete a generation cycle in under a week.
Spider mites are considered pests as they attack both indoor and outdoor plants. Controls can be put in place to reduce their impact, though the use of pesticides is discouraged; pesticide use often actually increases the population of spider mites as their natural predators are wiped out. Instead, natural predators of spider mites can be introduced to the area and allowed to prosper. Forcefully sprayed water is also a useful control, as this removes the dry and dusty conditions which allow the mites to flourish in the first place.