Professor James Parmiter (Bradford Dillman) drops his wife Carrie (Joanna Miles) off at her local church and drives off. She goes inside, having missed the start of the sermon, and sits down next to someone she knows who tells her she hasn't missed much. Indeed, the preacher has launched into his usual fire and brimstone lecture, and is in full flow when suddenly there is a tremor which quickly escalates into a serious earthquake, causing the floor to ripple and the rafters to collapse. It is over as soon as it began, but a large split in the ground outside has spewed up something strange - an unidentified species of cockroach with a notable talent...
Bug would be the last film famed showman and producer William Castle would make, yet for many of those who had followed his career, it wasn't the most auspicious note to end on. He had made his name with horror and science fiction movies throughout the sixties, and showed no sign of changing tack now, co-writing the script with Thomas Page, the author of the novel this was based on, The Hephaestus Plague, to contribute to what was in effect one of the most prevalent strains in the genre of the seventies, which was the revenge of nature film.
This had begun with Alfred Hitchcock's The Birds, and Castle was a great admirer of Hitchcock's, so it was only a matter of time before he got around to being influenced by him in a film that took creepy crawlies as its main villains. The bugs in question here emanated from beneath the surface of the Earth, and had the power to create fire, using it to make ashes which they consume, but now they're topside they also have the unfortunate habit of blowing up trucks, sometimes with people inside them. The Professor is determined to find out more, and commences an investigation into the whys and wherefores of the critters' biology.
He discovers that they cannot reproduce (where did they come from then? This is never answered), so will probably die out soon enough, but as they are practically indestructable unless you manage to puncture them (whereupon they explode due to the difference in pressure up here) more research is needed. Especially considering the fact that they are attacking people, including the film's most famous scene where one unlucky woman answers a telephone and gets the cockroach hiding in the handset setting fire to her ear as an unwanted reward.
Oddly, though, this is not content to be a killer insects on the loose movie, and turns into a mad scientist one when Parmiter is compelled to create a hybrid between the fire bugs and the less deadly variation that we get on the surface. Why does he do this, when he knows it will give them the power to breed and become more prevalent, creating a far bigger danger than they ever were before? Search me, but as Dillman's committed performance shows, the Professor has gone round the bend. We could have suspected this when early on we see him talking to a squirrel (eh?), but now he has a deep bond with the cockroaches he has unleashed. There are hints that this is borne of setting Hell itself free on Earth, but the religious angle is fumbled and only amounts to its imagery, so no room for theological debate here, which may not be so bad. It's just that for all its calculated vileness, Bug is very silly and not much better than a fifties B-movie of the same type. Electronic music by Charles Fox.