When a tarantula, which has been injected with a special nutrient formula, escapes from a scientist's laboratory. it grows into a 100-foot beast that menaces the Arizona countryside. Professor Gerald Deemer (Leo G. Carroll) has been working on a special nutrient to help ease a predicted food shortage that is expected to come with the increase in human population. His experiments have been moderately successful but there have been some failures as a result. One day while he is gone, two of his colleagues inject themselves with the nutrient with disastrous results and die a few days later. One however goes mad and injects Deemer with the formula. During a struggle, a giant tarantula injected with the formula escapes its cage and grows even larger and starts to attack cattle as well as human beings.