A friend gave me a 4' high cactus that I think is a euphorbia trigona. It looks healthy with lots of small leaves that she said were flowers. There are some fine spider webs at the top of the plant. I don't know if there really are small spiders or if that's what spider mites produce. Should I assume they are mites and spray w insecticidal soap? Can it hurt the plant?
I am just expressing my own experience; I had this issue last year and at the local HomeDepot they told me to use 1/2 Rubbing Alcohol and 1/2 Water in a spray bottle and then spray all over the plant. I did it once a day for two days and all the spider mites were vanished for good.
Supposedly a little Alcohol does not harm plants.