Multiattack

The sand spider makes two attacks with its impaling legs and one bite attack.

Impaling Leg

Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 11 (1d12 + 5) piercing damage. If the sand spider scores a critical hit with this attack, it rolls damage dice three times instead of twice. If both impaling leg attacks hit the same target, the second hit does an extra 11 (1d12 + 5) piercing damage.

Bite

Melee Weapon Attack: +8 to hit, reach 5 ft., one creature. Hit: 16 (2d10 + 5) piercing damage plus 13 (3d8) poison damage, or half as much poison damage with a successful DC 13 Constitution saving throw.