They look like tiny grey bugs that crawl around on your plant leaves. They can be found on the underside of the leaf and often near the midrib of the leaf.  If you notice that your houseplants have become stunted or have yellowing leaves, this is a sure sign that they are infected with mites. If this happens, you should contact your local nursery for advice on how to deal with the problem. It is completely safe to use dishwashing liquid to control mites on your houseplants. You just need to make sure that you use the right dilution. It is best to use a 10-20% solution. A 20% solution means that you will be spraying your plants with 1 part dishwashing liquid to 10 parts of water. The dishwashing liquid will help to loosen up the soil so that the mites can be washed away.