The Spider is an enemy originally added to Dungeon Defenders 1 in the Mistymire Forest Quest for the Lost Eternia Shards DLC.
This arachnid foe can spawn in multiple locations in many levels,and all drop in locations in a level are set areas, including behind your defenses. This enemy has another dangerous ability, the ability to fling webbing at players and defenses, slowing them, making them take more damage, and making them deal less damage. The web balls they fling can be blocked using a reflect beam, and their webbing does not affect the Series EV's Physical Beam defense.
Since they drop in to the level from set points, prior knowledge of these locations means that smart defenders can build their defenses in a way to completely neutralize them (eg. Bouncer Blockade or Electric Aura)