I have become a bit of an expert of pulling spiders out of their webs and letting them hang on by a strand, and then carrying them over to my chicks. The chicks immediately see the spider dangling and gobble it up. I've successfully brought a few out from the house to the coop dangling on the silk haha. But I agree with Jaxon that spiders are great predators for flies as long as they aren't in the nest boxes, I just seem to have an overabundance so they might as well be a snack as well as a good predator.