Civilian Unit. Constructs improvements on the land, increasing the effectiveness of tiles when worked by a City's population.
Note that the Worker can also construct improvements on water tiles. Unlike in Civilization V, you don't need a separate water unit for this; simply embark your Worker and move it over the resource.
Workers cost 200 Energy to purchase.
If Colonists are the heart of a colony, then Workers are the blood. Workers allow a colony to utilize terrain by building improvements. Not only that, they have the ability to remove Miasma from terrain, increasing its usefulness. As a colony grows technologically, so do its Workers, who will eventually gain the ability to add Miasma or even build the Terrascape improvement.