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What the sources say

Common Hermit CrabPagurus bernhardus

Every figure, record and mechanism on the Common Hermit Crab profile was written from a source, and this is the working table behind it: 49 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Animal Diversity Web, University of Michigan

Pagurus bernhardus (common hermit crab). Animal Diversity Web, University of Michigan.

The page saysA scavenger
The source saysCommon hermit crabs are scavengers.Note: tagline
The page saysraps on rivals' shells to try to take over better ones
The source saysusing its chelipeds to rap its opponent's shellNote: tagline; WT: 'The aggressor will knock on the shell it wants, drawing out the owner' (claim below)
The page saysto try to take over better ones
The source saysCommon hermit crabs are more likely to exchange and fight over shells when a new shell confers an advantage, such as more space.Note: tagline; 'better' is ADW's 'confers an advantage'
The page saysNear-shore waters of northwestern Europe
The source saysCommon hermit crabs are found in the near-shore North Atlantic waters of northwestern EuropeNote: stats.habitat
The page saysrocky and shell bottoms, seagrass beds and sand or silt
The source saysmost types of seabeds, including rocky and shell bottoms, in sea grass beds, and sandy or silty sediments, but excluding muddy bottomsNote: stats.habitat
The page saysScraps of dead animals, plants and microscopic bivalves
The source saysmicroscopic bivalves, scraps of dead animals, and plantsNote: stats.diet
The page saysThe common hermit crab (Pagurus bernhardus)
The source saysPagurus bernhardusNote: body; scientific name only
The page sayshas a front encased in a carapace of three thick layers
The source saysThe cephalothorax is encased by a carapace consisting of three thick cuticle layersNote: body
The page saysa soft abdomen, the tail end, coiled to the right
The source saysThe abdomen is soft and coiled to the rightNote: body; 'the tail end' is a gloss for 'abdomen'
The page saysIt lives in the abandoned shells of animals such as edible periwinkles and dog whelks
The source saysThese crabs inhabit the abandoned shells of animals, such as edible periwinkles ( Littorina littorea ), flat periwinkles ( Littorina obtusata ), dog whelks ( Nucella lapillus )Note: body
The page saysIts last two pairs of walking legs are greatly reduced and hold the shell in place
The source saysTheir last two pairs of walking legs are greatly reduced, and are used to hold the shell in place.Note: body
The page saysAnimal Diversity Web records a maximum body length of 8 cm
The source saysmaximum body length 8 cmNote: body; ADW's maximum ('Range length 8 (high) cm'), attributed and kept as a maximum
The page saysan average weight of 7.3 g, within a range of 0.13 to 54 g
The source saysRange mass 0.13 to 54 g 0.00 to 1.90 oz Average mass 7.3 gNote: body
The page saysa shell that is too large does not give the best protection, and one that is too small restricts growth
The source saysa shell that is too large does not offer the best protection and a shell that is too small restricts its growthNote: body
The page saysAnimal Diversity Web says the crab is known to live for up to four years in the wild
The source saysCommon hermit crabs are known to live for up to four years in the wild.Note: body; attributed to ADW because no current source was found in two searches
The page saysCrabs may attack each other to claim a shell
The source saysIndividuals may attack each other in attempts to claim ownership of a shell.Note: body
The page saysthey trade visual displays: a crab either raises its body high off the ground or lowers it in submission
The source saysBefore any physical encounter, Common hermit crabs engage in visual displays. During aggressive encounters, they either raise their bodies high off the ground, displaying their chelipeds and walking legs, or lower their bodies in submission.Note: body
The page saysIf neither backs down, one crab may crawl onto its opponent's shell and rap on it with its claws
The source saysIf neither individual submits, the crabs may try to dislodge each other from their shells, an interaction known as shell fighting. One hermit crab will crawl onto its opponent's shell, hitting its opponents entire body, including its shell, and using its chelipeds to rap its opponent's shellNote: body; 'claws' for chelipeds (ADW: 'the first pair are enlarged claws (known as chelae)')
The page saysOver 500 raps have been observed in a single shell fight
The source saysover 500 raps have been observed in a single encounterNote: blockquote
The page saysAround half of these fights end with the attacker swapping shells with its opponent
The source saysAround half of such encounters result in the aggressor exchanging shells with its opponent.Note: body
The page saysLarger crabs, and those with larger claws, are usually more successful than small and medium ones
The source saysLarger crabs, and those with larger chelipeds, are usually more successful than small- and medium-sized crabs in these encounters.Note: body
The page saysShell selection has been extensively studied in this crab
The source saysAnother behavior that has been extensively studied is shell selection.Note: body
The page saysIt is able to remember shells it has rejected before
The source saysThey are also able to remember shells that they have rejected before.Note: body
The page saysA crab with no shell, or one in a shell that gives too little protection or space, decides to move very quickly
The source saysIf a crab is naked or in a shell that does not offer enough protection or space, then it will make the decision to move into a shell very quicklyNote: body
The page saysfrom the White Sea to the British Isles, and as far south as Portugal
The source saysfrom the White Sea to the British Isles, including the North, Baltic, and Barents Seas. They are found as far south as PortugalNote: body
The page saysIt lives on most seabeds, including rocky and shell bottoms, seagrass beds and sandy or silty sediments, but not mud
The source saysmost types of seabeds, including rocky and shell bottoms, in sea grass beds, and sandy or silty sediments, but excluding muddy bottomsNote: body
The page saysIt is most often found at depths up to 80 m
The source saysCommon hermit crabs are most often found at depths up to 80 mNote: body
The page sayseating scraps of dead animals, plants and microscopic bivalves
The source saysmicroscopic bivalves, scraps of dead animals, and plantsNote: body
The page saysit is known to turn cannibal when resources run low
The source saysthey are known to be cannibalistic when resources are lowNote: body
The page saysIt is nocturnal
The source saysCommon hermit crabs are nocturnal.Note: body
The page saysNot Evaluated
The source saysPagurus bernhardusNote: stats.conservationStatus. Quote only anchors the species name; ADW's 'has not yet been assessed' line is undated and not relied on. GBIF's copy of the Red List returns NOT_EVALUATED (code NE) for Pagurus bernhardus (Linnaeus, 1758), usage key 2224231, ACCEPTED, checked 2026-10-06; Crossref has no IUCN assessment DOI for the name (prefetch and a 10.2305 search 2026-10-06).
The page saysit is more likely to swap or fight over shells when a new shell offers an advantage, such as more space
The source saysCommon hermit crabs are more likely to exchange and fight over shells when a new shell confers an advantage, such as more space.Note: FAQ 1; the FAQ's ref is ADW, so its first sentence now comes from ADW rather than the Wildlife Trusts line the body already uses
The page saysEven the final larval stage, which does not feed, has to seek out a suitable shell to complete its change into an adult
The source saysMegalops do not eat and must seek out a suitable shell in which to complete metamorphosis.Note: FAQ 1; megalops is the glaucothoe/megalopa stage before adulthood
The page saysOver 500 raps have been observed in a single shell fight
The source saysover 500 raps have been observed in a single encounterNote: vibe.reason animal clause; same quote as the body claim
The page saysweightKg: 0.0073
The source saysAverage mass 7.3 gNote: task #1096: 7.3 g = 0.0073 kg, ADW's average mass; Micro class, where the name guess gave Light. Not in a curated matchup

Source
02

The Wildlife Trusts

Hermit crab. The Wildlife Trusts.

The page sayslives in an empty sea snail shell
The source saysHermit crabs live inside empty sea snail shellsNote: tagline
The page saysdown to 150 m
The source saysThey can be found on rocky shores and down to depths of 150m.Note: stats.habitat; the current Wildlife Trusts page (150 m) replaces ADW's older 'may be found as deep as 200 m'
The page saysRapping on a rival's shell to try to evict the owner and take its home
The source saysWhen two hermit crabs meet, one may attempt to steal the other's shell by forcibly evicting the current owner.Note: stats.superpower; 'rap' is ADW's word (claim below); 'try to' keeps WT's 'may attempt', since ADW says only around half of shell fights end in an exchange
The page saysThe Wildlife Trusts give its body length as 3.5 cm
The source saysLength of body: 3.5cmNote: body; the current institution page, stated at its own scope
The page saysAs it grows, it moves into ever larger shells
The source saysAs they grow, hermit crabs move into ever larger shells.Note: body
The page saysThe Wildlife Trusts describe the aggressor drawing the owner out and fighting until one emerges victorious
The source saysThe aggressor will knock on the shell it wants, drawing out the owner and fighting it out until one emerges victorious.Note: body
The page saysThe Wildlife Trusts record it from rocky shores down to 150 m
The source saysThey can be found on rocky shores and down to depths of 150m.Note: body; current page replaces ADW's 200 m
The page saysIt is the largest of several very similar hermit crabs, and it is often found in rockpools
The source saysThe common hermit crab is the largest of several species of very similar hermit crabs and is often found in rockpools.
The page saysLook for a reddish brown body and a right-hand pincer that is larger than the left
The source saysTheir body is reddish brown and right-hand pincer is larger than left.

Source
03

Walsh, Arnott & Kunc 2017

Walsh, Arnott & Kunc (2017). Noise affects resource assessment in an invertebrate. Biology Letters.

The page saysthe crabs approached the shell faster, spent less time investigating it and entered it faster
The source saysWhen exposed to noise, crabs approached the shell faster, spent less time investigating it, and entered it faster.Note: body; abstract only
The page saysWhen researchers exposed crabs to anthropogenic (human-made) noise during shell selection
The source saysWe experimentally exposed hermit crabs to anthropogenic noise during shell selection.Note: body; abstract only

Source
04

Crump et al. 2020

Crump et al. (2020). Microplastics disrupt hermit crab shell selection. Biology Letters.

The page saysIn one experiment, 64 female crabs were kept for 5 days in tanks with polyethylene spheres or with no plastic
The source saysWe kept 64 female hermit crabs in tanks containing either polyethylene spheres ( n = 35) or no plastic ( n = 29) for 5 days.Note: FAQ 2
The page saysthen moved into poor shells and offered a better one
The source saysWe then transferred subjects into suboptimal shells and placed them in an observation tank with an optimal alternative shell.Note: FAQ 2; abstract only
The page saysCrabs that had been with plastic were less likely to contact the better shell or enter it, and took longer to contact and enter it
The source saysthey were less likely than controls to contact optimal shells or enter them. They also took longer to contact and enter the optimal shell.Note: FAQ 2; abstract only

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.