Ankheg Queen

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) slashing damage plus 10 (3d6) acid damage. If the target is a Huge or smaller creature, it is grappled (escape DC 15). Until this grapple ends, the ankheg can bite only the grappled creature and has advantage on attack rolls to do so.

Swallow. The ankheg queen makes one bite attack against a Medium or smaller creature it is grappling. If the attack hits, that creature takes the bite's damage and is swallowed, and the grapple ends. While swallowed, the creature is blinded and restrained, it has total cover against attacks and other effects outside the ankheg, and it takes 10 (3d6) acid damage at the start of each of the ankheg queen's turns.

If the ankheg queen takes 20 damage or more on a single turn from a creature inside it, the ankheg must succeed on a DC 10 Constitution saving throw at the end of that turn or regurgitate all swallowed creatures, which fall prone in a space within 10 feet of the ankheg. If the ankheg dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 15 feet of movement, exiting prone.

Acid Spray (Recharge 6). The ankheg spits acid in a line that is 60 feet long and 5 feet wide, provided that it has no creature grappled. Each creature in that line must make a DC 15 Dexterity saving throw, taking 21 (6d6) acid damage on a failed save, or half as much damage on a successful one.