Mariana,

It might be any old spider, but if you didn't see any it also could be
spider mites, in which case you'd need to treat. Personally, I've never
seen a spider mite, but I've seen their webs. Maybe run some soapy (Ivory,
or even 409) water with some alcohol through the mix and spray the plant
with the same stuff. Won't hurt if it's not mites.

Diana