Long-Eared Flutterfires appear to be a specific type, species, or sub-species of Flutterfire.
Flutterfires are Nanodragons that greatly resemble butterflies. The Long-Eared Flutterfire in particular has two long up right ears, or possibly horns, sprouting from its head.
Unlike some Nanodragons, Flutterfires can speak Dragonese. Like other Flutterfires, Long-Eared Flutterfires eat insects, as well as flower nectar. The latter produces a euphoric drunken craze, like Cat-nip does with cats.
Long-Eared Flutterfires appear in this reference book in the "Nanodragon" chapter.
In this final book of the Book series, Long-Eared Flutterfires appear on the Isle of Tomorrow along with Ziggerastica. They and other Nanodragons raise Hiccup off the ground so that he appears to be hovering of his own volition.
Perhaps the Long-Eared Flutterfire inspired the Deathsong in the Dragons: Race To The Edge TV Series.