It probably has to do with the fact that worms do tend to come to the surface in the early morning hours. Birds, which feed on the worms, start stirring around dawn, at first light, foraging for food. It would make common sense that the birds there first (the earliest) would get there pick of worms. Or, if worms were scarce, the earlier bird would tend to get the worm that was available. At some point, someone probably noticed a bird or two squabbling over the last worm that was available, and came up with the quaint saying "The early bird gets the worm". Many of our proverbial sayings have their foundations in everyday observances by people who notice a connection with such things and connect it with events in peoples everyday lives. Of course, that doesn't mean each and every time the bird is early, there will be a worm sitting there waiting for him. It just means the earlier you are, the greater your chances of procuring whatever it is you are after.
It signifies that one who puts himself ito the race first can be able to take a better lead as compared to whom they are late. but as seeing from the vision of science we can say that, worms must come out of their burrows as to fulfill thier need of warming their-selves or in the expectations of food at the morning.
Biologically The early bird gets the worm has no real meaning, it is used just as a quote.But to think logically it means that birds eat worms and the earlier the birds start to hunt the ealiest bird will catch the worm, and also it is a biolociall fact that worms go up the surface at the very morning.
Hope this helps.