The early bird catches the worm means that the person who arrives early will be successful. Example: "I always come early to work. The early bird catches the worm!"

When birds are competing to catch one worm, the bird that arrives early will catch the worm. Example: "From now on, I am waking up at six. The early bird catches the worm."

At times there is only one "worm" and only one "bird" can catch it, so the bird to arrive early catches the worm. Example: "My brother started investing money when he was 16 years old." Reply: "The early bird catches the worm."