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.
Great Britain was rich in coal and iron therefore the Industrial Revolution began there and impacted the whole country in a successful way. Consequently, changes during the late 1700's and early 1800's took place for all Great Britain workers.