Bog devils is a derogatory name for the crannogmen, the reclusive people who dwell in the swamps of the Neck. The crannogmen are collectively referred to as bog devils by their enemies, specifically the ironborn. They are seldom seen but always lurking.
Bog devils are associated with effective guerrilla tactics and most especially their poison arrows. The poisoned arrows of the bog devils need only scratch a man, and a few hours later he will be squirting and screaming as his life runs down his legs in gouts of red and brown.
The bog devils poison the arrow shafts and are said to smear them with feces and worse things. Even when a man is grazed by a poisoned arrow and his wound treated by boiling wine the poison can still take effect, and cause him to die a slow and horrible death.
A Clash of Kings
A Storm of Swords
At Moat Cailin Victarion takes to wearing chain mail day and night to protect him from the poisoned arrows. He reasons that sore shoulders and an aching back are easier to bear than bloody bowels.
A Feast for Crows
A Dance with Dragons
Ramsay Bolton sends Reek to Moat Cailin to offer the ironborn food and safe passage in return if they surrender unarmed. On the way Reek passes the rotted carcass of a horse, an arrow jutting from its neck. As he approaches arrows fly at him from unseen attackers in the bog, but he is able to enter the gatehouse without harm. 
The ironmen's departure is slow going, and Reek hopes he would die quickly, instead of suffering like Ralf Kenning did. For whatever reason, the bog devils choose not to let go their arrows on the column of ironborn as they make their way to Ramsay Bolton, who flays and impales the sixty three men that night.
Known bog devils
Those slain by the bog devils’ poison arrows
|“||Whoever wins the Seastone Chair, I shall deal with the bog devils.||”|
|“||The ones that die fighting will be the lucky ones. The ones who live will be given to the bog devils.||”|
|“||At Moat Cailin the bog devils had loosed poisoned arrows at his men, but that was to be expected from such degraded creatures.||”|
- ↑ 1.0 1.1 A Feast for Crows, Chapter 18, The Iron Captain, p 288.
- ↑ A Dance with Dragons, Chapter 20, Reek II, p 258.
- ↑ A Clash of Kings, Chapter 24, Theon II.
- ↑ A Feast for Crows, Chapter 11, The Kraken's Daughter.
- ↑ A Feast for Crows, Chapter 18, The Iron Captain.
- ↑ A Dance with Dragons, Chapter 20, Reek II.
- ↑ A Dance with Dragons, Chapter 20, Reek II, p 255.
- ↑ A Dance with Dragons, Chapter 56, The Iron Suitor, p 749.