Spider mites are not insects but arachnids—think spiders, scorpions, etc.). However, unlike most of their cousins, they do not feed on animal protein. Rather, they damage plant cells by piercing them to feed. These are VERY SMALL and are often not noticed until their population has exploded.
Though small, these little bugs can do a lot of damage and even kill your plant if they get out of hand. The first signs are brown or yellowing spots on leaves. These are often paired with protective silk webbing which is generally located on top of or under leaves as well as “nooks and crannies” of the plant.
Spider mites can be active year-round but are generally more numerous during the early spring and late fall, depending on your area.
This family exhibits cosmopolitanism—which is just a fancy word that means they are spread throughout the world in appropriate habitats.
Most spider mite species prefer arid and warm environments but can survive under many conditions. They are also known for their hitchhiking tendencies (shoes, shirts, plants, hair, etc.) and are often introduced to gardens this way. They become a major pest because of their incredible reproduction rates. During their short lives, females can lay up to 100 eggs or more and exhibit a form of parthenogenesis. This means the eggs do not have to be fertilized by a male to hatch!
To correctly identify the little buggers, you will need to magnify them 10x-15x using a jewelers loop, magnifying glass, or microscope. There are many pesticides available to treat spider mites but they are becoming less effective due to resistance after prolonged use. During overwintering months, make sure to pull any surrounding weeds to prevent future population explosions. There are also many beneficial insects such as predatory mites, lacewings, and minute pirate bugs that are commercially available to control spider mite populations. Insecticidal soaps and oils can also be implemented for severe infestations. Though they are not as effective as some pesticides, they pose less risk to wildlife and people.
There are around 1,200 species of spider mites and they feed on a wide range of plants. Several species, such as the two-spotted spider mite (Tetranychus urticae), feed on hundreds of plant species and are widespread throughout the world.