I  am wondering why spider mites would be on a hard surface. Did you mean spiders not spider mites? Spider mites are so tiny you can hardly see them and they make webs on the back of plant leaves. Mites can be killed with spray of insecticidal soap if the infestation seems out of control. Perhaps if you sent a picture of the problem I could identify what type of spider or mite you have. Keep Growing, Marianne Binetti