What is the name of the venomous snake in 'The Speckled Band'?

The venomous snake in The Adventure of the Speckled Band is called a swamp adder. In the story, Sherlock Holmes identifies it as “the deadliest snake in India” after it returns through the ventilator and fatally bites Dr. Grimesby Roylott.

The snake is part of Roylott’s elaborate murder method. He has arranged Helen Stoner’s bed beneath the ventilator, installed a useless bell cord, and trained the snake to cross from his room into hers. He uses a saucer of milk and a whistle to control it, hoping to kill his stepdaughters before they inherit money.

Doyle’s swamp adder is fictional. The story’s description combines traits associated with real snakes, and modern commentary often notes that the Indian cobra comes closest to the creature’s appearance and behaviour. A rattlesnake, viper, or cobra is therefore not the canonical answer, even though a cobra may be the closest real-world comparison.

The story was first published in The Strand Magazine in February 1892 and later collected in The Adventures of Sherlock Holmes.