Spider mites are very small and may go unnoticed until plants are severely damaged. Water stressed plants, plants that need and are not receiving humidity and dusty leaves are susceptible. You may first notice damaged foliage appearing speckled or beginning to turn yellow due to the mites sucking the juices before you see the tiny spiders. Be careful not to confuse the fine webs for dust and be sure to inspect the undersides of leaves. Know you have an infestation before you treat. Mites have super tiny, pale yellow to reddish eggs laid on the under sides of leaves. The mite bodies are most likely going to be brick red in color (sometimes brown, yellow, or green and the two spotted, depending on the species). Mites are tiny and you may need a magnifying glass to see them. Hold a white paper under a suspicious leaf and give it a tap. If tiny red dots fall you have spider mites and you may see them scurrying about now that they have been disturbed. Loss of leaves and plant death can occur if mite populations are not controlled before becoming a serious infestation.
Control: Isolate infected plant(s) and cover any tables or carpet, etc. that may receive any over-spray if using soap or oil sprays.
Begin with a gentle shower of water to see if you can knock them off this way. Inspect every 4-7 days and you may find another shower necessary. This may need to be repeated for a month or more.
You can gently wipe leaves, both top and undersides, with a damp cloth to remove mites rather than a shower if you have a large, heavy pot that is difficult to move.
You may decide to spray your plant with a mild soapy water solution, thoroughly soaking both sides of the leaves. Then rinse with clear water (a gentle shower) the following day. Always use room temperature water. It will be necessary to do this once a week for a month or more but be sure you have insects before treating. There are some plants whose leaves are sensitive to soaps in which case you will see brown spots on the leaves after application and you should not repeat the procedure. Crown of thorns, Jade plants and Gardenias are some examples. Some ferns, palms and succulents may also be sensitive. You can test a small area first if unsure.
The use of an insecticide will be of no use because spiders are not insects!
You can use a homemade insecticidal soap spray made from garlic, onion and red pepper or homemade insecticidal oil spray made from clove or rosemary oils or infusions. You can make your own in your kitchen.
There are specially formulated pesticides for spiders, called acaricides, which are plant based from the oils of garlic, mints, rosemary, cinnamon, etc.