As I learned, Guy N. Smith was indeed a real author, and these are indeed real books. Smith was born in Staffordshire, England in 1939, and when not chronicling the tales of crab attacks, was also a rabid shotgun enthusiast, who wrote for several gun publications including a stint as the gun editor of The Countryman's Weekly. He also won the British pipe smoking championship in 2003 (no, that's not a euphemism), and even wrote a book on Tobacco culture.
But mostly, he is remembered for his crabs (plus a few werewolf books). It all began with Night of the Crabs in 1976, in which a legion of colossal crustaceans terrorize a tranquil Welsh beach town, Jaws-style. Killer Crabs followed two years later, although the plot summary doesn't tell me anything other than "big crabs, attacking people." One year later, Smith revealed The Origin of the Crabs. The series continued in 1981's Crabs on a Rampage, in which giant crabs, uhhh, terrorize a beach. While that might sound redundant, Crabs on a Rampage is also one of the more well-reviewed installments, as Smith decided to cut out the fat, focusing the story on the things the fans wanted most: giant fucking crabs, killing people at the beach. Crabs' Moon, which came out in 1984, tells a parallel tale to the first crab book. 1988's Crabs: The Human Sacrifice focuses more on the horror of a Lovecraftian cult of crab-worshipping humans, rather than the titular crabs themselves (reviews for this daring literary experiment are mixed).
Then, Smith took some time away from the crabs. But they returned with a vengeance in 2012, with the aptly named Killer Crabs: The Return, which took their adventures down under to Australia!
Sadly, Smith passed away from complications involving COVID-19 in December 2020. Although he does leave behind a helpful non-fiction book on how to write horror fiction, which I am now very much looking forward to. Because knew the inherent truth of nature: we all become crabs eventually.