You know the old joke of Slasher films having “30 minutes with jerks”. This film is more like “90 minutes with jerks”.
The plot is, in a nutshell, generally amiable though not particularly handsome Northern Guy goes to rural (mistake 1) Southern (mistake 2) town to meet a nice girl he’d previously met and engage in some tourism and fishing (Strike 3, you’re out!)
However, a recent thunderstorm has downed some power-lines, and the electricity has somehow caused earthworms to mutate into bloodworms and has sent them on a killing spree. Because Science!
This is also where things fall into problems. Everyone in town is written as assholes, because this is a nihilistic 1970s exploitation film, and the only belief we have in humanity is that humanity is terrible. Most of the townsfolk are stock archetypes (the sheriff is Neglectfully Evil Southern Sheriff #2, the rest of the town is Obnoxious Redneck #3, and the love interest’s mother appears to have been grabbed right out of The Glass Menagerie).
The thing is, the killer worms concept works – that’s the premise of Slither. In fact, I would argue that Slither is the core concept of this film done better, so go watch Slither instead. Or watch the MST3K episode with Squirm.
Also, the movie poster for Squirm is scarier than the film is.