Giant Ant

Giant Ants refer to unnamed insect-type monsters that spawned from the many caves located in the Ant Hill on the 46th Floor of Aincrad in Sword Art Online. They had high attack power, but very low Hit Points (HP) and defense stats, making them vulnerable to players who can avoid their attacks.

Appearance
These creatures took the appearance of abnormally big ants with sharp, gigantic mandibles, which they used to attack the player.

Attack Patterns
The monsters' attacks consisted of using their mandibles to bite the player as well as spitting mucous acid from the mouth.

Red-Nosed Reindeer
Kirito fought several of those monsters as a way of leveling up, but after six hours hunting the ants, he could no longer react or counter their attacks as before. Despite this, Kirito eventually reached level 70.

Trivia

 * Because of how quick the monsters can be killed, they were a very efficient way of gaining experience.
 * A giant ant's weak point was a specific part of its belly.