Wurm Siege

Wurm Siege is a ranged monster skill used by the gigantic Siege Wurms of the Crystal Desert, the Chaos Wurms of the Ruins of the Tomb of the Primeval Kings and the Infernal Wurms in the Fissure of Woe. Wurm Siege fires a slow-moving projectila that explodes with a large area of damage centered on the target. Players nearest the center of the attack take the highest damage (60 health with 60 armor) and players on the fringe get the lowest damage. Wurm Siege deals Earth damage. The explosion is similar to that of a Trebuchet's.

A Siege Wurm's aggro circle is aproximately twice the size of a character's aggro circle. Similar to a Longbow attack, Wurm Siege has a range outside of the Siege Wurm's aggro circle (specifically, it has a range of roughly 3 to 3 1/2 aggre circle radii). So, if a player aggravates the Siege Wurm and then pulls out of its range, that may not be enough to prevent the impending explosion.

Wurm Siege is curiously considered a Spell and has no energy cost, a 3 second casting time and no actual recharge time, however it does appear to have an aftercast delay of approximately 6 seconds. You can simply interrupt it to avoid being blown up. Skills such as Distracting Shot being particularly effective. Also, Diversion can be used to shut down the Siege Wurm entirely for an extended amount of time.