Every time Cacnea came out of his Poké Ball, he would latch onto James, out of affection, which would hurt him with his spikes. He met him right before he released Weezing, and he saved them from a Pokémon hunter. Cacnea was still following James and the others to open the box he had given to him. Not that long after Weezing's release, Cacnea joined James's Team. Later when Jessie and James were in Sinnoh, James decided to leave Cacnea with Gardenia to master his Drain Punch move.
Cacnea was James' first Pokémon caught in the Hoenn region.
Cacnea has some similarities with Ash's Bayleef. They are both Grass-Types, they both insist on hugging their trainers after being sent into battle, both cause problems when this happens, and both made an appearance in the Sinnoh region.