Spiders do not eat or "kill off" plants of anykind. They are predators of other
spiders and small insects and build their webs where these creatures can be
found. If you have spiders, they are there because you have some other insect.
You more likely have an infestation of spidermites. These are not spiders but
got their name because of the webbing they produce. They do destroy plant
tissue. See:
http://www.colostate.edu/Depts/CoopE...s/spidmite.htm
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