The Mayfly is an infiltration technique, which is a signature characteristic of White Zetsu and its clone siblings, due to being infused with the cells of Hashirama Senju.
It allows him to merge his body with the ground and flora and travel at very high speeds; however, it is noted not to be as fast as Space–Time Ninjutsu such as Kamui. His insectivorous plant-like shell has the ability to merge with the ground, because it is tinged with his chakra. Then, using the underground network of organic matter, consisting of things like plant roots and water veins, he can travel everywhere with high speed. Using this technique he can conceal himself in such things as trees and even sand. Once merged, his presence is completely concealed, making it almost impossible to detect him, even for sensor type ninja like Karin. This makes this technique perfect for close-ranged spying.
If a White Zetsu does not wish to leave its location, it can connect itself to the nearby network of plant roots in order to send messages to other Zetsus.