The Far Harbor hermit crab still resembles its unmutated pre-War ancestor quite closely both in appearance and in its habits, with only one major difference: its immense size. Towering head and shoulders over any human, hermit crabs are far too large to protect their vulnerable abdomen by squeezing it into an empty gastropod shell. Instead they use wrecked vehicles to facilitate their ambush hunting style.
Hermit crabs are giant creatures on par with fog crawlers, mirelurk queens and super mutant behemoths, though not quite as tall as the latter. As rare as they are powerful, the crabs are only ever encountered alone in a select few locations on Far Harbor Island where they masquerade as a wrecked Lobster Grill van choked with tires, mud and debris. Should something or someone venture close enough, the hermit crab will reveal itself and attack with its massive claws. The process of extracting itself from its shell takes quite some time and should usually suffice to put some distance between the Sole Survivor and the crab, provided the creature did not get the jump on its prey.
Needless to say for a beast this size, hermit crabs are heavy hitters and can inflict immense damage with their claws while soaking up massive amounts of firepower in return. Fortunately they are quite slow and not exactly agile. They also can neither fit through doors nor mount obstacles. However, they do have the ability to create hatchlings that pour out at the player in waves. They will stop, pull halfway back into their shell and begin shaking before releasing about 4-6 hermit crab hatchlings at a time. Sometimes they will do that upon death as well.
Hermit crabs usually do not attack until suitable prey gets within four to five meters of their position. They will, however, reveal themselves and actively start searching for trespassers if one stays in the general area for too long. This happens even when the player remained hidden during this time.
Hermit crab hatchlings are, for all intents and purposes, identical to mirelurk hatchlings. They look similar (except the color of the skin), show the same behavior and are equally weak in combat, although low-level players should not underestimate them when encountering them in larger numbers.
Due west of the Oceanarium, at the farthest end of the destroyed bridge
A short distance due north of Waves Crest Orphanage, between two derelict pickup trucks in front of a Vim vending machine
Just in front of the north screen of Eden Meadows Cinemas, assuming the resident ghouls had previously been taken out
Far Harbor settlers may invite the Sole Survivor on a hermit crab hunt in the quest The Deadliest Catch. The target is most often one of the crabs mentioned above (usually the one closest to the settlement where the quest was obtained), provided the creature is still alive at that point.
Hermit crabs can be hard to spot with the naked eye, especially when approaching them from any direction but their front side. To prevent getting ambushed by a monstrous crab far away from any body of water, quickly checking suspicious Lobster Grill vans with VATS can save one's day. A power armor helmet equipped with a Targeting HUD will also identify any hidden hermit crab immediately.
Another, somewhat more dangerous check involves looking for a civilian suitcase that is stuffed between the tires inside of the Lobster Grill van. If there is one, then the wreck is harmless. If not, prepare for combat.
Hermit crabs do not seem to have any defense against radiation (whether damage or poisoning) whatsoever. As such, a gamma gun, radium rifle, or irradiated legendary weapon can eliminate one in fairly short order.
Encounters with hermit crabs appear to be unique occurrences for any given location. If they respawn at all, it takes significantly longer than usual.
Dead hermit crab hatchlings can be found scattered throughout Far Harbor, one being on the barrel in front of Longfellow's cabin. Whether they are food for the inhabitants or just random scenery remains to be seen.
Because of the Lobster Grill vans hermit crabs use as shells, Penetrator is extremely useful against them.