A body has been found in the desert, and Sheriff Andrews (Nestor Paiva) doesn't know what to make of it. The local doctor, Matt Hastings (John Agar), arrives in town and no sooner has he reached his office than he is being telephoned by Andrews and told to meet him over at the morgue. What could be so urgent? wonders Matt until he sees the body and diagnoses the cause of death as acromegalia, a condition that affects the pituitary gland and causes abnormal growth. Yet the dead man was seen a month ago looking perfectly healthy, and acromegalia simply doesn't progress so quickly...
It was not, as you might expect from the title, the bite of a tarantula that caused this anomaly, but our old friend in science fiction films mad science. The real villain is actually the misguided Professor Deemer (Leo G. Carroll, earning himself a mention in the Rocky Horror opening song), and he didn't mean to cause the havoc he does, but it was in the service of the advancement of mankind he carried out these acts against nature, and it is mankind who is going to pay. Not that he was alone, as the dead man was one of his assistants.
An assistant who got a load of his serum that he had been injecting into animals to make them bigger, but when you give it to a human that fast-developing acromegalia, as they call it, is the result and will kill you in a few days. What precisely the purpose of doing so in the first place is unclear, as Deemer explains that he was wanting to make bigger animals for some tasty ways to solve the upcoming food shortage he foresees occuring in the near future, and the only result they could have hoped for with human subjects would be an amazing colossal man or somesuch.
Well, he doesn't get that, but he does get his other assistant, also afflicted, to go on a rampage at the remote lab and inject the Prof with the serum after smashing up the project as best he can. Deemer buries his body in the desert, but it is too late for him - and too late to catch the certain tarantula which has got away after its case was smashed and is now free to roam the countryside. Naturally with a Jack Arnold film that means lots of desert scenery (he would return to giant spider menaces with The Incredible Shrinking Man soon after), and a nice, eerie atmosphere to go with the not-too-bad special efects.
Every good monster movie needs a damsel in distress, and here the role is filled by Mara Corday as "Steve", short for Stephanie and indicating she's operating in a man's world as Deemer's new research assistant. Naturally, she and Matt get to know each other and a romance develops so that the last minute rescue from the eight legged freak can be all the more impressive, but the film spends quite a lot of time on relationships and pussyfoots around showing us any spider horror for most of the first two acts. Keeping the suspense levels up or saving on the budget? You be the judge. As with most of the fifties creature features, you're not intended to feel too sorry for the monster, so nobody cry when Tarantula die, although you may be able to recognise pilot Clint Eastwood flying to the rescue. Not one of the great Arnold science fiction epics, but diverting all the same.