Like its Chocobo Eater cousin, Earth Eaters are dangerous. At the beginning of battle Earth Eaters are not overly aggressive, preferring to hit once or twice with an occasional biting attack. At this stage, Earth Eaters are immune to every status ailment. When staggered it will lose most of its immunity, but the stagger will be short.
After the first stagger Earth Eaters can cast "I Don't Feel So Good...", an area-of-effect attack that can inflict Deprotect, Debrave, Defaith, and Poison on Lightning. When its HP is reduced to 60%, it will bestow itself with Haste, Bravery, Vigilance, and Veil.
At this stage Earth Eaters will start hitting multiple times, attempt bite attacks, and start doing swallowing attacks. Once its HP is depleted further it will do successive debuff attacks, which will apply the effects even when blocked. The debuff attack will also add Pain in addition to the status effects listed above.
The player should be prepared before fighting an Earth Eater. A Saboteur-type schema is of little use due to Earth Eater's initial immunity, and its relative resistance to Poison. A defensive schema will aid, but being aggressive is usually the better option.
The player should aim to stagger it as quickly and as often as possible. Earth Eaters are most vulnerable after bite attacks and swallowing attacks. While the first stagger is short, Earth Eaters often pause for an extended amount of time, allowing the player to inflict damage. The self-buff afterwards will represent a threat and should be removed quickly. The swallowing attack is first initiated by a roar that will interrupt Lightning's action, making her vulnerable for the main attack; the player should guard as soon as the Earth Eater opens its lower mouth.
A mage-type schema equipped with Chaos's Revenge, or a Dragoon-type schema equipped with spears (and optionally, Locket Pendant) is effective at staggering Earth Eaters. Since Earth Eaters cast Veil as part of their self-buff, using Dispel is not recommended. Instead, the buffs can be stolen via Brave Thief (either by equipping Battleaxe of the Believer, Warrior Hunter's Mask, or Mage Hunter's Mask) to remove the Earth Eater's buffs and award them to Lightning.
While the area-of-effect debuff attack does not do much damage and can be blocked easily, the debuff effects will always apply if the Earth Eater does it successively at later stages of the battle. Using Evade twice bypasses both the damage and the debuffs. Evade in combination with Guard can be helpful, as the damage taken from guarding will pile up, whereas Evade, if done with proper timing, can avoid most attacks.
If the player has Fang as a party member, and wishes to use a Saboteur-type schema to augment her abilities, Deprotect should be used after the first stagger, as Earth Eaters will be vulnerable after that point.
Cyber Jump Suit, Ghostly Hood, and any item that reduces physical damage, can make a battle with Earth Eater (as well Chocobo Eater) a piece of cake, as Lightning becomes invulnerable to physical attacks. It can be combined with Aerora to stagger it easier. Heavy Slash with level 3 or higher in a Soldier of Peace garb is also powerful. The player should return to Cyber Jump Suit when Earth Eater recovers from stagger, otherwise Lightning can be affected by the status ailments. Just in case, the player can keep some Remedies or Mega Remedies in the recovery items slot.