Mechanical Spider

A metal spider is an Automaton made by Hephaestus. They constantly trigger Annabeth's Arachnophobia.

The Lightning Thief
In The Lightning Thief, a swarm of metal spiders attack Percy and Annabeth while they are at Waterland.

The Battle of the Labyrinth
In The Battle of the Labyrinth, Eurytion gives Percy, Annabeth, Tyson, and Grover a metal spider so they can find Hephaestus.