I found this posting about getting rid of spidermites for you:
It has been suggested that spraying plants with a 1:1 mixture of alcohol and water will kill spider mites on contact. Rubbing alcohol, like any alcohol for any creature, is poisonous in high dosages, and it evaporates quickly doing little damage to the plant it's been sprayed on. Some people suggest a 1:3 mixture of rubbing alcohol to water, but the strong the mixture, the more certain you are to get as many mites as possible. Make sure to cover the entire plant, focusing on the bottoms of the leaves where spider mites tend to hang out.
If all else fails, miticides are, of course, one of the most effective forms of spider mite treatments and the fastest way to get rid of spider mites, usually. It all depends on the kind of miticide that you choose. Some of the most common miticides are Avid, Kelthane, and just about anything that contains pyrethoids. These chemicals should be applied once every five days until all signs of spider mite infestation have gone. Again, people gardening vegetables and herbs should try every other avenue before using miticides, including the biological mite controls described below
Sounds like spider mites. The natural remedy are insects called "phytoseiulus persimilis" If you want to go that route, you can Google it, the insects are sold online. Once the phytoseiulus persimilis have eaten all of the red spiders, they die themselves. You have to buy more phytoseiulus persimilis to replace the others in X amount of days (you'll see that info. online) to kill the spiders that hatched from the spider eggs.
If you want to go the chemical route, you can purchase sprays at Walmart that will kill spider mites, but you will have to spray every so many days in order to get new spiders that have hatched, just follow the instructions on the can.
You said the spiders were "in the ceiling" of your front porch. If they actually are inside it, the sprays probably won't reach there, but the phytoseiulus persimilis would be able to get them there. If all else fails, there is always the exterminator.
Add your voice to the conversation. Click here to answer this question.