Mirelurk

Mirelurks are creatures living throughout the wastelands.

Background
Mirelurks are hostile creatures. Ada mentions the mirelurk is an irradiated, "hyper-evolved horseshoe crab" that functions in a caste-like system. Moira Brown classified them as Scylla Serrata Horrendus and questioned if they had evolved from crabs or some sort of brine shrimp. John Hancock states that mirelurks were much smaller before the bombs dropped. Porter Gage refers to mirelurks as "mudcrabs."

Mirelurks nesting below inhabited decks are considered a nuisance for inhabitants of Rivet City, regularly exterminated by the city's security team. They lay eggs in small clutches and grow quickly, used as food and traded throughout the wasteland. Mirelurks are sensitive towards high pitched noises, such as those occurring in Vault 92 and on Spectacle Island. Mirelurks are heavily armored and resistant to most forms of damage, but their faces are vulnerable. Mirelurk kings have the ability to cloak themselves in order to ambush unsuspecting prey.