Complex sentence: The Domestic house spider is common in both Britain and the pacific northwest of the Americas, indeed it is thought to have been introduced into the Americas by British Colonists who would have unwittingly provided it passage across the Atlantic.
Split into simpler sentences: The Domestic house spider is common in both Britain and the Pacific Northwest of the Americas. Indeed, it is thought to have been introduced into the Americas by British colonists who would have unwittingly provided it passage across the Atlantic.