The Bikochu beetle.
The Bikochu beetle (微香虫) is an insect that was once used by the Aburame clan in the Great Ninja Wars. It was becoming an endangered species, however, so they let it live in a special bug habitat, uninhabited by humans. Two of the female's distinguishing traits are its long nose and its blue eyes, but a giant bug-like creature that looks exactly like it is sometimes confused with the real thing. It also has an incredible sense of smell, stronger than even a dog's.
The species only lays eggs once every few years during a certain breeding season; a day following a rainstorm. Soon after one hatches, it goes into the pupa stage. After this, it is not long before it metamorphoses into an adult. Bug users are drawn to the Bikochu because of the fact that the first scent that the beetle detects after its metamorphosis stays in its memory, so whenever it smells it again it tries to get to the source of the scent. This is what makes Bikochu beetles coveted, since it can be used as a formidable tracking device.
In the filler arcs, Tsunade sent Naruto Uzumaki, Shino Aburame, Kiba Inuzuka, and Hinata Hyūga to find it in the hopes of locating Sasuke Uchiha. At the same time the Kamizuru clan was pursuing it also, to restore their clan to its former glory. The Leaf ninja managed to retrieve an egg, but Naruto farted right after it metamorphosed. Sakura Haruno was not happy with the news, and used the Bikochu to find and punish Naruto.