Skulltula

Skulltulas are recurring enemies in the Legend of Zelda series. They are sizable spiders that exist in many dark and discreet places, such as caverns or temples, inhabited by other malevolent creatures. A mark in the shape of a skull appears on their abdomen, which seems to be an admonition all for all those who may come in contact with the creature to stay away if they wish for their own safety. When Skulltulas spot a trespasser, they attack it by dropping down from the ceiling with their web.

The Legend of Zelda: Ocarina of Time and Majora's Mask
In Ocarina of Time, the backsides of Skulltulas are vulnerable to sword strikes; they can also be defeated if Link hits one with his Hookshot or by shooting an arrow with his Fairy Bow.

In Majora's Mask, Skulltulas' front sides are invulnerable to Hookshot strikes; however, they can still be dispatched with the Hero's Bow. They are not as frequently encountered as in Ocarina of Time. However, the first regular enemy encountered in the game is a Skulltula, which appears inside the Bombers' Hideout.

The Legend of Zelda: Twilight Princess
Skulltulas have a different attack pattern in Twilight Princess. They attack by crawling towards Link and using a biting attack. Also, their exoskeletons offer much more protection than before. However, they can easily be dispatched by attacking their heads, either with stabs of a sword or with basic, non-jump wolf attacks. Once stunned, Skulltulas can be defeated with the Ending Blow. Once Link learns the Back Slice, it can be used to great effect against Skulltulas.

Interestingly, in an early demo at the Electronic Entertainment Expo, Skulltulas were shown to be able to tie Link up in a web and attack, but this was cut from the final product.

The Legend of Zelda: Phantom Hourglass
Skulltulas appear in the Ghost Ship dungeon. This incarnation of Skulltulas does not feature their trademark hardened shells. While they can be killed, a new one will appear instantly after a Skulltula has been defeated; a room can never fully be cleared of Skulltulas. When Link unknowingly aids the Diabolical Cubus Sisters, they appear to fear these creatures; however, knowing whether or not it is part of the act is not possible.

The Legend of Zelda: Spirit Tracks
Skulltulas appear within the Lost Woods in the Forest Realm, and inside the twisted tunnels of the Sand Realm. As the Spirit Train approaches, they drop down in front on the Spirit Tracks using their webs. If Link does not kill them with the cannon, or scare them away with the train whistle, the train will crash right into them and take damage. They are almost twice as big in this game as the biggest Skulltulas from Ocarina of Time, but are less frequently seen than in most games. There is also a more persistent kind that appears later on, resembling a Gold Skulltula, which will not flee at the sound of the whistle and takes two hits to kill.

Etymology
"Skulltula" is a portmanteau of the words "skull," referring to their skull-like carapace, and "tarantula," a variety of arthropod.