Most spiders are passive hunters, relying on the insects the eat for fly into their webs. A few are hunters, Wolf Spiders for example, but most are beneficial, though passive, insect controllers in the garden.
Spiders will eat Whitefly, if they fly into the spiders web.

I love seeing spiders and their webs in my yard. I call them friend, even though they are afraid of me! They are doing good work in helping to keep the balance. The orb weavers, with their big webs and a "zipper" down the middle, just adds to the beauty. You might want to search the internet to find out what kind of spiders you are finding. I usually start with "pennsylvania spiders" (or pennsylvania butterflies, etc.) and see what info I can get.

OK-they stay!