Be careful if you decide to use chemical pesticides.
1) They are often incredibly toxic to marine
life. Even tiny quantities in water
(and i do mean tiny) can cause widespread death.
2) Spiders are generally much more sensitive to pesticides than the pest species, such as roaches, ants, termites, flies, mosquitos etc. so you may end up making the situation worse by killing all the spiders and then having nothing to keep the other populations in check. The answer to this problem is NOT to use even more pesticides, as the pest species will then develop a resistance very quickly indeed.
Provided there are not hundreds (or thousands!) of them and that they are not a species that is capable of doing you actual bodily harm i would leave the spiders well alone and let them do their thing. If there are hundreds of them, ask yourself why there are hundreds of them in the first place! They must have a food