The Giant Pet Ant is formerly one of the bullet ants that Scott Lang controlled during his fight against Yellowjacket that was accidentally enlarged with one of the Pym Particles Disks. Cassie Lang kept the ant as her pet.
The Giant Pet Ant was a normal-sized ant that lived in Cassie Lang's room before it was called to battle Darren Cross by Scott Lang. During the fight, it was accidentally enlarged and ran out of the house, scaring those outside who mistook it for a "messed-up looking dog."
Cassie Lang kept the ant as her pet, hiding it from her family and feeding it with scraps during a family dinner where her mother, Maggie, and Jim Paxton invited Cassie's biological father, Scott Lang, as a sign of gratitude for having saved Cassie from an insane Darren Cross.
- The Giant Pet Ant's existence ignores the square-cube law; the Giant Pet Ant would be crushed under the weight of its own exoskeleton.