The term mouse fly is kind of a contradiction and one of the types of flies that brings the word fly in fly fishing almost as far away from something flying as possible - still surpassed by shrimp flies not to mention crab flies, but anyway...
One of the reasons Britain became rich was because the Industrial Revolution (factories and such) got off the ground there sooner. Britain had a large navy, and many colonies in other parts of the world, such as India, and Rhodesia.
For example, in the 1700s most of England's population lived in a rural areas; however by the 1800s most of England's population lived in a urban area. Thus, it can be said that the Industrial Revolution eventually transformed England from a primary agrarian society to an industrial one.