This movie was the top half of an all Roger Corman double-feature with Not of This Earth. ACM was not as imaginative of a story, but managed to be somewhat offbeat from the usual radiation-generated giant critter sub-genre. While it does have the requisite giant animal, per the title, there is a semi-mystical element that keeps things unusual as the scientists disappear one by one. It flirts around the edges as a ghost story.
Quick Plot Synopsis
A plane lands a group of scientists on a remote Pacific island. They are replacements for a mysteriously missing research group sent to study the effects of nuclear test fallout. The plane explodes on take off, trapping them there. There is too much radio interference to call for help. Earthquakes and landslides rock the island. A deep pit appears near the cliffs. That night, Martha hears the voice of one of the lost scientists calling her to the pit. Carson hears it too, so they investigate. Carson falls in. While the others go via a sea cave to look for him, Martha and Dale go back to the house. A giant crab attacks the house (next room), eats their lab mice and deliberately smashes their radio. The next day a better equipped search party for Carson. While in the caves, a cave-in wounds Jules. That night, feverish Jules hears the voices calling him to the pit. He goes and a giant crab claw gets him. Others awaken at his scream. Jules' voice says he and Carson are fine, come to the cave. So, they all do. (?) A giant crab attacks them. Grenades and bullets are useless, but a stalactite falls, piercing the crab's brain. A second giant crab escapes. The scientists take a claw back to study. The molecules of the flesh can move like a liquid, so bullets simply pass through them. Electricity, however, turns it to dust. The crabs are able to create great heat too. Hence the tunnels, pits, earthquakes and downed plane. They are also making the island smaller. Soon no place to hide. Mutated by radiation, the giant crabs absorb life, include their victims' consciousness. Growing ever smarter and more powerful, they plan to dominate mankind. (a female crab has an egg brood). Trapped on the rocky mountain peak (all that's left of the island), Hank powers up the radio transmitter antenna. He topples it across the crab just before it gets to Martha and Dale. Hank and the crab die amid the massive sparks. The end.
Why is this movie fun?
It is part ghost story, with the 'spirits' of prior victims enticing the living to join then. The pacing is pretty good. Despite the huge logical gaps and obviously low budget, the mood of impending doom works pretty well.
Cold War Angle
As per usual, radiation from nuclear tests created the monsters. Symbolically, these monsters absorb people who then try to recruit others to join their collective. This could be taken as either communism or McCarthyism.
Hand of God? -- ACM opens with a turbulent cloudy sky and a God-like narrator reading Genesis 6:7 -- the verse where God tells Noah that He's going to wipe out the earth. "And I will destroy man..." This opening Bible verse isn't tied in well. Were the life-absorbing crabs God's judgement on nuclear-sinful mankind? If so, it wasn't a very divinely powerful judgement. Was it a blanket caution that nuclear man is bringing this and other troubles upon himself? Other than it being somewhat customary to open a sci-fi film with a Bible verse, there's no connection.
Energy Monsters -- Radiation changed the molecular make-up of ordinary land crabs (whom we are told were ruthless). They absorbed the energy of their victims as well as their minds, Apparently they were able to absorb chemically potential energy too, such as the missing dynamite. They were also able to direct energy (beams?) to down planes and bore tunnels. This last feature is somewhat like Godzilla's atomic breath. These were not simply big critters, as were the giant ants in Them! ('54). They were highly intelligent (though ruthless) energy monsters.
Budget Beast -- The actual crab monster models are predictably low-budget looking. Corman shows a bit too much of them. Their obvious prop-model status keeps ACM from rising into higher 'thriller' status. But, they did what they could with the budget they had.
They're Not After Our Women -- The poster pushes the usual button that the monster is out to capture our prime females. A few scuba scenes tease at setting up the poster image, but it never happens. The crab monsters never pick up Pamela Duncan in their claws.
Gore Rising -- Two scenes in ACM show the inroads that screen gore was beginning to make. Early in, a headless sailor is hauled into the rubber boat. In the cave-in scene, a stalactite severs Jules' hand, which lay just beyond his arm. Gore for sensationalism was becoming more common in the horror genre and was starting to show up in sci-fi.
Evil Collective -- ACM almost fits into the alien-takeover sub-genre. The 'absorbed' colleagues ceased to be individuals and became part of the 'new' order. Atypically, they became part of a single physical 'thing' but with separate consciousness. In line with the sub-genre, their personalities changed. Instead of friends, they became proponents of the new order, seeking out their colleagues to be absorbed too. This 'turning' fits the existing mood (fear) of communism.
Electronic Savior -- Once again, good ol' electricity saves the day. No conventional weapon could kill the crab. High voltage, however, does it's usual magic. This plot device was already a bit threadbare by the mid-50s. Nonetheless, it won't be the last time our friend the kilowatt saves our day.
Poor Russell -- Once again, Russell Johnson plays the tragic hero. As in This Island Earth ('54), he gives his life to save the male and female leads. Retirement to Gilligan's Island may have seemed relaxing.
Bottom line? If plot holes, cheap props and marginal acting bother you, it may not be enjoyable. If you're a Corman fan, or an aficionado of 50s radiation-mutant-critter movies, you'll enjoy ACM.