The first group consists of the true Gondwanian derivatives. These mayflies have descended from those widespread throughout ancient Gondwanaland and their closest relatives are found in Africa-Madagascar, South America and Australia as well as southern India. The second group is northern in origin and its closest relatives are found in Europe and the Palearctic Region. The third and largest group probably evolved in the Oriental Region and have spread to Sri Lanka from there. Related species are now found in Africa and other places as well.
Mayflies are dependent upon clean water for their habitat.
They are extremely sensitive to the quality of the water in which they live. Polluted or extremely silty streams often have a dearth of mayflies. I found this to be especially common in many of the streams which ran through tea plantations. There is no ground cover among the tea bushes and the red soil readily runs off into nearby streams after heavy rains. Similar nearby streams which did not receive the silty runoff had a healthy mayfly fauna.