D: Jeannot Szwarc. S: William Castle, Thomas Page. Novel: “The Hephaestus Plague” by Thomas Page. P: William Castle. Cast: Bradford Dillman, Joanna Miles, Alan Fudge. US Dist (DVD): Paramount.

By the time of this, his final production, producer William Castle’s ballyhoo machine had definitely run out of steam; Bug’s gimmick of a million-dollar life insurance policy on star cockroach Hercules is a bit of a puzzler. While Bug may lack the prestige of Castle’s biggest production, Rosemary’s Baby (1969), it’s a more-than-respectable science fiction chiller (and is certainly director Jeannot Szwarc’s finest hour). Bug boasts solid performances, an unsettling electronic music score (atonal bleeps and howls by Charles Fox, better known for Barbarella and “Killing Me Softly With His Song”), and an unusually adult approach to its subject.

An earth tremor opens up a fathomless crevasse in a farmer’s field, disgorging a lethal new species of cockroach from the lower depths. With chitinous shells strong as steel plate, they’re almost impossible to kill – and their unique ability to raise fire from an odd little contraption by their rear legs scores them extra marks for creepiness. Bred for life at much higher pressures, they’re slow-moving and have a tendency to explode if pierced in the right place; but they’re also smart. Very smart. They solve their transportation problems by crawling into vehicle exhaust pipes, and the nearby town is soon reeling from a spate of inexplicable wildfires. (The bugs feed on ashes. See, it makes sense.) High school science teacher (and keen entomologist) James Parmiter (Bradford Dillman) begins to make a study of the creatures, quickly realising that they’re all about to peg it since they can’t survive at ground-level pressures. But once Parmiter’s friends – and then, his own wife – fall victim to the scheming bugs, Parmiter loses the plot and starts experimenting with ways to keep the wee critters alive…

The pervasive tone of nastiness is quite surprising, given the MPAA’s PG rating. The bugs-versus-moggie incident will leave cat-lovers ashen-faced, but the demise of Parmiter’s wife (Joanna Miles) is even tougher: the sight of her hair suddenly igniting, then of her body thrashing in flames, is genuinely shocking. Dillman’s subsequent grief (and descent into craziness) carries tragic conviction, a testament not only to his performance but to Szwarc’s downplaying of the aftermath; we simply see Dillman huddled in the darkness of his lab, surrounded by the wreckage of his experiments. His state of mind is all-too-easy to infer. What’s less understandable, at least to this reviewer, is Dillman’s decision to perfect the killer insects, interbreeding them with regular roaches to breed a super-race of flying horrors. Bit of an own-goal, that one. But if all mad scientists behaved rationally, what fun would that be?

Bug lacks the visionary intensity of its immediate rival, Saul Bass’s Phase IV (1974), which even in its cut theatrical form emanates an almost messianic quality. Bass also had the sense only to use genuine insect performers in his microscopic cast; by contrast, Bug stumbles badly in its final act with Dillman unconvincingly menaced by woeful plastic-toys-on-wires. All the stylised lighting in the world isn’t going to help make that look anything but cheap and silly. And the business with the bugs spelling out messages to Parmiter on the wall (“WE LIVE”) is a bit daft. Still, the climactic shots of Dillman ablaze – in which you can clearly glimpse the actor’s face behind the flames – are persuasively shocking, ensuring the film ends on a plausibly grim note.