There are more mentions of ‘Crab the Dog’ than ‘crab the crustacean’ in Shakespeare’s works. The canine variety is found exclusively in The Two Gentleman of Verona, being the name of Launce’s faithful friend, albeit as “the sourest-natured dog that lives”. After all, Crab the Dog gets his name from the resemblance between his nature and that of the crab-apple tree, Latin ‘malus’, whose sour fruit would be the first object to come to the mind of an Early Modern man upon hearing mention of ‘crabs.’
The sour taste of the crabapple reappears in King Lear, where the Fool compares Goneril’s nature to the bitter fruit, saying that “She’ll taste as like this [i.e. Reagan] as a crab does to a crab”. Petruchio, being called “a crab” by Katherine the Shrew, presumably because of his resemblance to the notoriously gnarly produce of the tree, turns the insult on its head by retorting, “Why here’s no crab, and therefore look not sour.”
The lack of aesthetic appeal to the crab-apple powers what Nathaniel – with his tongue firmly in cheek – describes as the “sweetly varied” language of Holofernes, the schoolmaster who compares the fall of a shot deer to “a crab on the face of terra, the soil, the land, the earth” in Love’s Labour’s Lost Whilst Holofernes speaks bastard Latin, it is a rather different question of heredity that the crab-apple points up in Henry VI pt II, when Suffolk accuses Warwick’s mother of infidelity:
> SUFFOLK Blunt-witted lord, ignoble in demeanour!
> If ever lady wrong’d her lord so much,
> Thy mother took into her blameful bed
> Some stern untutor’d churl, and noble stock
> Was graft with crab-tree slip, whose fruit thou art,
> And never of the Nevils’ noble race.
With all this talk of crab-apple trees and their relation to sour dispositions, ugliness, disease and marital infidelity, it comes of something of a surprise to learn that when Hamlet talks of crabs, he is in fact the only character in all Shakespeare’s works to have the crustacean in mind. That said, he famously has a rather strange idea of the creature, madly telling Polonius that he could only resemble Hamlet “if, like a crab, he could go backward”.