Acidic spiders are non-attackable Araxyte that are summoned by Araxxor during the third phase and in the middle path, whenever the middle path is open. They are signified when a ranged projectile flies elsewhere which explodes and leaves behind a green ooze on the hit tile. After five ticks, the acidic spider will spawn, having a bar over it. When this bar fills, the acidic spider will explode, although no harmful effect will happen. The speed of the spider is random, as they may move one tile every 10% or move 4 tiles every 10%.
If an acidic spider manages to reach its target, it will explode instantly regardless of how much the bar above it is filled, and the player will receive up to 32,000 damage, likely resulting in an instant death. Resonance has no effect on this damage due to it being typeless, although the revival effect of Immortality will be activated, and Barricade will block the damage as normal. The effects of Saradomin or Zamorak warpriest armour and the Lucky perk can trigger on the explosion, but it is not recommended to rely on this as a means of saving the player from being killed.
They used to occasionally spawn in the Araxyte Lair graveyard where they would attack a gravestone every 4 seconds, depleting the timer by 15 seconds for each attack. This was removed by Jagex due to player complaints.