Poison Darters are Tree Dragons that appear in the How to Train Your Dragon Book Series.
Poison Darters are medium to large dragons that are dark green in color. They appear to have ear flaps and a bit of an under bite. In The Incomplete Book of Dragons, Poison Darters are portrayed with a nasal horn.
Poison Darters have excellent eyesight and sense of smell. They are one of the species of dragons that can shoot projectiles out of their fire-holes (Razorwings and Leviathorgans are two other species). As their name implies, their projectiles — or darts — contain poison that can render a human unconscious. This poison is strong enough to kill smaller animals.
Poison Darters can be trained but with much difficulty. The Berserker Tribe is able to do so.
The Poison Darter appears in this reference book, showing the different uses of a dragon's fire-hole. They also appear in the Dragon Key at the back of the book.