Keen Smell. The giant ant has advantage on Wisdom (Perception) checks that rely on smell.

Charge. If the rhinoceros moves at least 20 feet straight toward a target and then hits it with a gore attack on the same turn, the target takes an extra 9 (2d8) bludgeoning damage. If the target is a creature, it must succeed on a DC 15 Strength saving throw or be knocked prone.

Multiattack. The giant ant makes one gore attack and one bite attack.

Gore. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 14 (2d8 + 5) bludgeoning damage plus 22 (4d10) poison damage, or half as much poison damage with a successful DC 12 Constitution saving throw.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 5) bludgeoning damage and if the target is Medium or smaller than the target is grappled(escape DC 12). Until this grapple ends, the target is restrained and the giant ant can’t bite a different target.