Peacock Spider

Spiders in your house may seem like a problem, but spiders are your friends, in ways you may not even know! Spiders eat flies by the ton. Literally by the ton. If you were somehow able to continue your mission of killing spiders until every last one was squashed, smooshed, or otherwise obliterated, then you, my friend, would suddenly have a pretty sizable fly problem to deal with, as in millions and billions of flies and their babies, aka maggots, swarming around your face. Spiders keep the fly population in check, and also the mosquito, black fly, centipede, clothes moth, and every other nasty buggy population.

https://hubpages.com/living/let-spiders-live