Normal: "A relative of the fiends found in the Mi'ihen Highroad colony. Though similar in appearance, it avoids their communal lifestyle. It is adept at fire and lightning magic." Oversoul: "A relative of the fiends found in the Mi'ihen Highroad Colony. It avoids the communal lifestyle of the other bugs. Its specialty is magic and it can use chain attacks." — Scan
The Insect Matriarch is an enemy in Final Fantasy X-2. She is a rather powerful enemy, as she has high stats. She is even more dangerous when she Oversouls, as her physical attack is more than enough to kill any under-leveled character. It is best to deal with this enemy by using attacks such as Black Sky or Stone Breath to take her out quickly, and it is highly advised to set up Protect at the start of the battle.
An easier way to win the battle is to use Paine's Arsenic Knife. Insect Matriarch is not immune to its instant death attack, and it kills her in one shot.
In the Fiend Tale endings, a notable Insect Matriarch became a fiend out of disillusionment for humans and societies' rules. However, Insect Matriarch learns the hard way that fiends have their own rules like humans.