Ankheg

Melee Weapon Attack: +5 to hit, reach 5 ft.. Hit: 10 (2d6 + 3) slashing plus 3 (1d6) acid damage.
If the target is a Large or smaller creature, it is grappled (escape DC 13). Until this grapple ends, the ankheg can bite only the grappled creature and has advantage on attack rolls to do so.

Recharge 6. The ankheg spits acid in a 30-foot line (5 ft. wide), provided that it has no creature grappled.
Each creature in that line must make a DC 13 Dexterity saving throw, taking 10 (3d6) acid damage on a failed save, or half as much damage on a successful one.