Skulltula are a species of spider from Hyrule. They are very large, roughly the size of a cow, and have a protective plate on their backs shaped like a skull.
Skulltula are very dangerous, and have been known to kill people. Their protective shells are extremely hard and can not be punctured by any known weapon (not counting the Master Sword). They live in the forests of Hyrule, and are most common in the Faron Provence.
Their poison has been used by the Sheikah to arm their weapons with deadly toxin.