Geldarm

The Geldarm is a large anthropod-like insect that is common to the desert regions of The Adventure of Link and A Link to the Past.

The Adventure of Link
In The Adventure of Link, Geldarm is very tall bug that lives under the earth in desert regions. Geldarms emerge from below the surface and contract as their body receives damage. They are more of a path-blocking nuisance than a dangerous foe, but Geldarms still attack by spitting small stones towards Link. There is no trick to defeating these monsters, but beware as it can emerge out of the ground randomly to hurt Link. A few slashes with the sword to its head will be more than enough to destroy the Geldarm.

A Link to the Past
In A Link to the Past, Geldarms (called Hokkubokku in Japanese) look and act a lot like Pokeys. When Link strikes them with his sword, a body segment is broken off which bounces dangerously around the room. This can be avoided by attacking them with the Fire Rod, which burns the entire Geldarm in one attack.

Trivia
It is interesting to note that their Japanese name is "Gerudoarm," implying a connection to the Gerudo.