The Scarlet Beetle was an ordinary beetle mutated by the radiation of an atomic experiment. It gained conscious thought and the ability to command other insects. Receiving emergency impulses from his devices from his ants, Ant-Man decides to investigate what appears to be problems in the insect world. There he finds an irradiated beetle, able to communicate telepathically. The Scarlet Beetle plans to destroy the human race with the help of all the insects in his thrall (beetles, wasps, grasshoppers etc.)
Seeing Ant Man as a potential obstacle in this plot, he orders his insects to capture him, remove his helmet and toss him in a pit that he cannot climb out himself. Stealing Ant Man's Pym Particles, the Scarlet Beetle exposes itself to Ant Man's growth gas and grows to human size. He then orders the insects on a campaign of terror, attacking humanity at all levels: knocking down hydro poles, stealing dynamite, and striking people ill with spider bites. Meanwhile, although not on Ant Man's head, his helmet sends out a signal that alerts his ants of his location, the ants arrive and help Ant Man out of the pit. Regaining his helmet, he and his army of ants face off against the Scarlet Beetle's army of assorted insects, defeating them with honey, a water fountain and DDT spray. Furious that his army was so easily defeated, the Scarlet Beetle is goaded into chasing Ant Man into a nearby toy store. Inside Ant Man manages to fight off the Scarlet Beetle long enough to secure a javelin from a toy knight and use it to pierce the shrinking gas canister that the Beetle wore around its body. Exposed to the gas once more, the Scarlet Beetle reduces back to his original size and is easily defeated by Ant Man who traps the Beetle inside a deflated balloon. Having the Scarlet Beetle decontaminated of radiation, it resumes its normal intelligence and abilities, Hank Pym releases it back into his back yard. 
Telepathy: The Scarlet Beetle has a genius-level intellect and can command insects, arachnids, and other arthropods. He even can control human minds though it can only be one mind at a time. He has proportionate superhuman strength according to his size. 
Pym Particles: Using stolen Pym Particles he was able to grow to a gigantic size, with proportionate strength of an insect.