Though Worker Ant's stats are very low (1AP/1HP) it's a staple card to play in the early game, especially when using a green filler deck. Simply play it early along with many other ants, later combining it with Ant Colony and Orb of Unity. This is especially good when fighting an aggro deck-- the Worker Ant costs only 1 green energy and can be played on the first turn, giving you an effective defense while you play stronger allies. If you're looking to combo this with Orb of Unity, one of the strategies included in the pre-made green deck, make sure to play as many ants as you can (Ant Matriarch helps!).
Strong Against: Aggro decks, mediocre cards when combined with objects like Orb of Unity.
Weak Against: Killer Wave (the Wave will take out all of your allies, leaving you defenseless, which in a green deck is almost certainly a fatal blow).