Spike

Spikes are a type of trap block that deal 40 / 60 damage to players who come in contact with them. On the PC version, Console version, Mobile version, and tModLoader version, they additionally inflict the Bleeding debuff for 10 seconds. They can be found in the Dungeon and can be broken with a drill, pickaxe, or explosive. This is the only way to obtain them, as they are not craftable.

Notes

Spikes turn bright red when the Dangersense buff is active.
Spikes will deal damage to a player if any part of the player is in contact with them.
Just like Wooden Spikes, Spikes only damage players. They do not damage NPCs, critters, or enemies, and as such are unsuitable for base defense outside of PvP.
Spikes deal the same base amount of damage in all modes. Since defense is more efficient in Expert and Master Mode, the player will almost always receive less damage from Spikes than in Classic Mode.
Spikes are valid walls for NPC housing.

Spikes are the only pre-Hardmode tile that a Picksaw cannot mine in one hit. On the PC version, Console version, Mobile version, and tModLoader version, they are destructible in one hit by any pickaxe above 50% pickaxe power.

It has been requested that more images be added to this article.
Specifications: "Sprites prior to 1.4.0.1"

Desktop 1.4.2: Fixed an issue where Spikes would not hurt the player from some angles at certain elevations.

Desktop 1.4.0.1: Sprites updated. Damage increased from 40 to 60, and now inflicts the Bleeding debuff.

Desktop 1.3.0.5: Spike damage is kept separate from other damage when factoring immunity, preventing abuse of invincibility frames.