Though they are common, Octopus mercatoris are rarely seen.
The Caribbean dwarf octopus is mainly nocturnal, hunting by night and staying in a cave during the day. While most octopuses are cannibalistic, O. mercatoris is less cannibalistic than other species, and is sometimes found in small groups under rocks. They eat crabs, shrimps, and small fish.
This species has an average lifespan of 8–10 months. Because their eggs are large, they are sometimes kept and bred as pets.